I also have a pretty large classroom library. To be honest, it was pretty much trial and error when school first started. Therefore, every Tuesday the same 5 students are in the library. They can check out a book for the week and get reading carpets. I have 2 librarian who help in keeping the library neat and checking out books.
Every book has a sticker on it with a number.
I have master list on my computer that tells what book goes with each number. This way we can tell if some are missing and how much they cost. Inside the books, I have little pockets and cards - the same you would find in a regular library book. Students have to fill it out and give it to the librarian. The librarian is in charge of checking the books back in.