Definitely don’t do all your files at once, and take some time with a few albums to figure out what’s going on. Then you can plan how to tackle things.
Depending on how exact you want your tags, you may decide to manually check things before hitting save.
I would also recommend using cluster + lookup first instead of scan.
As well as being slower scan ignores existing tags, so if you already have things in their albums etc it can needlessly split up your files/ make things messy.
You could also use the opportunity to try some different audio players - iTunes has its own set of issues/limitations that come up around here every so often.