Save often and be ready to just reset when you run into random encounters of lots of red chocobos.

I've never ended the game with any generics in my game, but that doesnt mean I dropped them right away when I got a story character either since I don't think all of them are worth it. Classes I'd recommend you spend time in mastering/learning several abilities would mainly be monk, thief (used to steal some of the best armor in the game later), and ninja. There are obviously nice things to have here and there but I tend to put most/all of my characters into these classes and may then send them to learn other classes individually (for instance just have a couple learn a ton of white magic instead of just a cure, esuna, and raise).