There’s a ton of normalization programs out there that can batch convert entire collections, if you need it that bad. On Mac, I use a program called MP3Gain. But be prepared that it will tend to turn down the loudest as well as boost the quietest, so you’ll need a hair more boost at your mixer. And it also tends to boost songs that SHOULD be quieter (soft ballads, for example) a bit more than you might want. You’ll still need to tweak a bit once done.
Oh, and if you have embedded the lyrics in the file rather than just link to the text, it will store the new file without lyrics, so you’ll have to redo the lyrics save... So always best to adjust the file to the needed level BEFORE you embed lyrics, LOL
I wouldn’t worry too much about batch adjusters... for one thing, the better ones can create a folder of adjusted copies, so if there’s an issue, you can always use the old files, secondly the better ones can be set to only adjust a BIT up or down so you can gradually get where you want to go. And if the files are decent bitrate, the better ones don’t introduce any artifacts.
I’ve used them on folders with hundreds of files to balance to burn to CD’s and been pleasantly surprised at how good they worked. Basically, if your file collection runs to the thousands, doing it by hand is pretty much an impossibility...