How can I free up space on my iPod without losing songs?

okay so I've got a iPod Video 5.5 30GB that I got from a family member. it came not working but I put a new battery in and boom. there is so many songs on there like its all songs like 28-29gb of songs. I will listen to the songs, but I also want space for movies and whatnot. I just think the family member downloaded lots of versions of songs. There is like 3 copies or more for each song, some iTunes bought, overs from CDs, some rare editions, some live versions, and I don't want to lose them as they are there and there only (even some songs from when he used to be in a band in the 90s-2000s). this morning I did plug in the iPod, showed hidden files and copied over the Music folder to my desktop. there was folders in there with names from F1 to F49. I command-A'ed x49 to put them in my library. there was nothing else in my library at the time btw. checking my storage weirdly it said there was only 27.??gb of music while on the iPod nearly 29gb. is there some kind of extra data on there or is it possible I missed a folder? or did some of it not copy over? it mean the files make so sense so I guess there's no way of knowing but like. I just kinda want to idk like sync the iPod fresh and just put all the songs on there once... some of the songs in Apple Music don't even have titles and are those weird names with album art and some don't play etc. I really need the extra storage space, but like bro I don't even know what this is about. I guess it's possible I have the actual files on my desktop but like what if they didn't copy over properly?? I just need advice honestly. anything will help

[Re-Titled by Moderator]

Original Title: idk what to title this just any advice will help please