The 'modern library' include many varied collections of data. They are not just a book or written material collection! Computers (internet connected), video and audio streams, along with written materials are to be expected in almost good libraries. Then add in 'special interests' based on topics and the modern library becomes complex and to use it effectively, one need some organization to make it work.
Almost all ham operators begin to build a small personal reference library of electronic and HAM related information. What materials do they collect? What seems to be the most popular and of actual real use to a ham? Almost all ham libraries will have miscellaneous materials from the ARRL, probably the most popular being "The Radio Amateur's Handbook". This book(s) has a wide coverage of information, basic to advanced materials, with the addition of construction information from most of the different areas in amateur radio. Also, it contains varied reference data on many current electronic components {a major reason to watch hamfests for older copies ~ not just historical construction ideas and concepts}. Then home libraries include various other books from the ARRL like: "ARRL Antenna Book"; "Basic Radio"; "Understanding Basic Electronics"; "Basic Antennas"; "Ham Radio for Arduino and PICAXE"; and etc. A good subset appears to be always prominent. There are many other suppliers of technical books of special interest to the ham radio operator - just start searching the internet to find these sources. It seems that electronic books and files stored on computers are the mainstay future direction. Many CDs can be stored and used much easier than several bookcases each with multiple shelves and offer benefits of electronic searching thru the material. Now(2023), CDs and DVDs are being 'phased out' and becoming 'old tech'. But there is no assurance that the older material is going to be freely found 'in the cloud' - so one must choose a direction to meet there own needs. I seem to migrating to 'large' external hard drives and 'very large' thumb drives (multi-TB sizes).
Do not forget to checkout your local library to determine what you may like to parse and you can usually use them for free. Sometimes state or private libraries and college libraries can add to the variety of the material. The ability to checkout materials may be an issue, but I have never had an issue with using the materials inside any library. Sections on 'engineering works' can be extensive. I use a local University's engineering library quite frequently and make a small annual donation back to the university. As I am not a faculty member or student, I have no 'check-out' option, but the material is there! However, over time some of the older books seem much harder to locate (are they being removed?)
The internet and your personal computer system allows for quite a large collection of materials. The major issue rapidly becomes one of organization of all the information. Computers do add a great feature - "searching". Finding materials becomes much easier when computer searching is available.
The form (media type) of the materials one wishes to collect in a personal library needs some very serious consideration. There is the historical favorite of a 'paper collection' in the form of books, magazines, data sheets and catalogs (mine spans over 50 years - "before computers/written" through "only electronic publishing (hard drives)"). As a collector, I can attest that the collection can get very large and heavy, I have several hundreds of pounds of paper reference material in my collection. The space required is a consideration. Some key items will deserve your consideration, I would strongly suggest electronic storage versions for most of your collection, I have about 200 computer CDs (files) of various ham materials. I have four external hard drives in the TB size and five TG thumb drives. This form of material is much more easily organized and is definitely easier to search. CDs are falling out of favor, but still seem to be the most cost effective method for me (2021 and still in 2023). Also, information from the internet can be easily added to this format. Note: I have been buying older hard drives and placing them into 'external drive cases'. I have copied a large number of "CD files" in my library over to these drives. Still only a thought here, but thinking a 'server' unit with a Raspberry Pi would allow for personal 'file server' setup at a relative low cost and eliminate the physical exercise of physically reconnecting drives.
I suggest you join the ARRL just to gain free access to the entire QST magazine collection (Plus the three other ARRL Magazines), plus the many other benefits of the ARRL are very helpful. The entire magazine collection is searchable and easily referenced and will provide information on almost any topic of ham radio. This eliminates the storage of these magazines (I have physical copies of QST from 1967 through the current issue).
ARRL members may now receive digital access to all four (4) ARRL magazines. Joining 'QST' and 'On the Air' on a digital platform are the bimonthly editions of 'QEX' - The Forum for Communications Experimenters and 'NCJ' - National Contest Journal. All four are available free online from the ARRL Members page for all active members.
The SARA {W8QQQ} crew has a detailed instruction page at: ARRL Online Publications. There are many, many benefits to joining the ARRL, but this is one of my personal favorite perks that membership provides. The ARRL has a large amount of free information to anyone interested, but with the addition of a membership, additional information availability is added - that is a huge benefit to joining. Also, the ARRL membership is good for the support of the hobby in general. It is a large organization that will not follow all your personal choices of direction, but overall membership should be carefully considered. Some individuals do not agree with some ARRL policies and do not wish to support the organization. While I respect their ability to choose, I think they would be better served to join and work within the organization to bring about a change. In a large organization it is impossible to align policy to all the different individual's desires, but that is not a valid reason to pass the overall benefits.
I have a very favorite site to start looking for reference material on almost any topic, http://www.wikipedia.com. You can use their search function to find large amounts of information on most topics. A large amount of reference material on components is available. Start searching a topic on Wikipedia and then look at the "references" being used (at the bottom of the topic). Use these references as an additional list to look further online or use a physical library. Wikipedia should never be quoted as a 'reference' directly. Errors can and do exist in the data, but it often provides a great starting point in it's stated references and certainly leads into strong supported reference materials being used.
Perhaps a 'little off topic', but important to any Web user is the work of Wikimedia Foundation. A nonprofit organization that supports 'free' knowledge projects. Their mission is "access to free knowledge for every single person". See the footer on their site link to see all the projects they are working on... not just the main Wikipedia page! When used together they can fill-in the knowledge base for many areas.
Depending on your interests, you may consider other ARRL specialty magazines: QEX ~ electronic experimenter; and NCJ ~ National Contest Journal for contesting information. Consider ham radio magazines (in general, but I am sure there are others, but let's start here): QST; CQ Amateur Radio; Popular Communications; CQ VHF; World Radio; Nuts and Volts; and many older magazines, 73 and Ham Radio for example, are available on computer CDs (and on the internet). Many magazines are no longer being published, but the older issue hold a wealth of technical knowledge and ideas. Watch out for club newsletters, many can be found online for free and can be a good source of information. Professional technical magazines can be used for additional information. Checkout the military training manuals for radio and electronics, many are available online for free.
Computer files for mathematics, electronics, computers, robotics, antennas and mechanical construction can be of interest, this should include component datasheets and many sales catalogs for ham equipment. You can learn quite a bit from reading all these materials. Take your time and read as much as you can in multiple sessions, your knowledge will grow exponentially as you move forward. It seems the more you learn, the faster you learn the details. Just remember it is a hobby and should be taken on as a happy experience. Oh, lets not forget the 'online tutorials' that are available, these may or not be considered 'library' materials but are great for expanding your knowledge.
When adding the computer hardware and software magazines, the knowledge base increases. They have a variety of topics, many of which are electronics related and some directly connected to ham radio. Computer programming in many different computer languages from machine code to full graphical and sound programming, add in artificial intelligence, vision coverage and the scope becomes very large. Learning micro controller and micro computer topics can give added enjoyment.
Library Cost is something you may wish to consider. If you spend money on your library that money is not available to your electronics equipment purchasing. [All these 'real life tradeoffs' are yours to make.] To help keep library costs lower, watch hamfest tables and used book places for books that may be of interest. Learning to use spreadsheets to enhance your information organization is highly encouraged. The spread sheet can be used as a simple database for sorting through your information and as a mathematical calculation aid. There are free programs that allow you to read Excel sheets and free spreadsheet programs for your use, try Open Office. Also, there are other programs (cheaper) that will work with your files (I use 'Think Free'). As always, learning as you grow makes the information gathering and organizing process relatively painless. It also helps control the cost factor.
Keeping large amounts of information organized can become difficult. I suggest you look in the SARA Web Links (or Web Search) and find the software program link for 'AZZ File'. This is a shareware spinoff of an old Microsoft Word Index Card file, but it is on serious steroids! Think of a 3" x 5" card system (they can be expanded to much larger sizes) with categories of topics, terms, or whatever and the individual card containing detailed information on a category. Think of several different stacks of these card systems for different types of information (each like a set of file cabinets). The detailed information on the cards, can be text, equations, web links, pictures, reference titles, sound or video files, etc. Each collection of cards can be 'viewed' and provides computer searches for any terms or words. That is the general concept of AZZ File. I am sure if you look at the program, you will find many, many uses for it. It can be your personal ham data reference 'library card file'. I find I use it for several of my hobbies, not just Ham Radio. I am sure you will enjoy this program if you give it a look! I have azz files for 'Web Links' that I pass across. I continue with: 'I've seen it on the Web' and cannot remember exactly where and the 'search engines' have collected, so much material that you can not find the one site you want (where was it?). Well if you 'AZZ card it', you can search much closer to where it was at. Throw in a topic and keywords along with the link for the site on a card and 'Wow, there it is'. thus the following hint. It is great for "YouTube Video links", I use titles, authors, time to play and the exact Web link - any become search enabled.
Hint: Make sure to copy the reference spot (hyperlink) where/whenever you get information and put on a card(s)... you will want to find it again and this saves a large amount of your time in trying to find your original source! Setup an AZZ file for your viewed Web links. AZZ Cardfile is a very nice program and is super easy to use. If you use it 'PLEASE' consider purchasing a license... support the shareware concept when you can. I have used this program for years and greatly value it's features.