Regarding inputing all the data from the beginning.
It is a lots of work and you could even call it a hobby. Well, you could call it a full time job, too. It takes a lot of time. A lot.
I find it useful, but that may vary for you depending how pedantic you are deep inside. I make sure that everything is in a certain way (correct letters in each language, German, French, etc.), that artists do not show up in multiple iterations, that there is no "various artist" anywhere, and other obsessive little things. A tiny mistake may make your 12-song album end up being an 11-song album with another similar album with only one song.
Even with all that work, every now and then I find imperfections, but those are easy to fix. Having a "blank" library that you have to straighten out is a different thing. Approach with caution.
In case you have any number of classical recordings, automatic tagging from the Internet exists, but it is so imperfect that I find it useless. Looking for, let’s say, Mahler’s 5th symphony may produce and omit a number of recordings. There is almost a guarantee that they will not all show up on one list. At least not on a few different devices that I have. Looking for Mozart may give you a few Mozarts. Mozart; Mozart W.A.; W.A. Mozart; Wolfgang Amadeus Mozart; Mozart, Wolfgang Amadeus; etc. If you are looking for a certain movement, another messy search. Getting all the symphonies tagged in a certain way is a chore, but definitely was worth it for me.
Good news, Pink Floyd is easy.
Converting (dBpoweramp) from AIFF to FLAC loses some of the less-important tags. Converting exactly the same thing from FLAC to AIFF retains them. Go figure.
Just the fact that you embarked on putting cover art on all of your files makes me think you do like to have things in some order. Basically, you are at some risk of eventually tagging more than just covers. Once you browse through your album covers and find two Dark Side of the Moons, you are in trouble. That is how I started. 20 000 or so files later, I think it was worth it, but am warning you it takes time.
Of course, while you are doing it, back it up in multiple locations. Hard drives are cheap these days and not having a few copies of your work may end up being very frustrating once something fails.