Well, there are a good amount of battles that can make you want to restart, in this game.
The universal golden rule of FFT: Keep two save files. There are times when you will have to undergo a series of battles, and the game will prompt you to save inbetween this series of fights. Some fights may require more preparation beforehand, and if you're stuck in a save where you can't go back out to level up/get more abilities, then you may be finished. But with two save files (one inside the set of battles, one before the battles begin), you can avoid this by going to your earlier save and prepare for the upcoming battle (*cough*Wiegraf*cough*).
As for teams...well, it's all up to you. I mostly used melee characters, and usually the special characters (I only used two mages with Math Skills for my generics). Some of the special characters are quite powerful, once you recruit them.