How should I train my characters? (GBA)

[SS2 Vegeto]

This will be my first time playing through the whole game, and I would like some advice on how to go about training the characters. My first concern has to do with armor. Which characters should I equip with what kind? I know that for pure mages, it's best to choose the armor with the lowest INT/SOUL penalty, but what about a paladin-type character, for example? What sort of range should the penalty be kept within for a fighter who doubles as a white/black mage?

My second concern has to do with magic. I would like to teach Firion at least a couple of elemental spells, but I'm not sure how well that would work out with Maria as my black mage. Is a paladin with some elemental spells just a bad idea? If so, is there another way that I can make it work? Also, what sorts of magic do you recommend teaching to the characters outside of the original party? Are there characters that I should just not bother teaching any magic, or are there some spells that it always helps to have access to?

Finally, I've heard that weapons carry no INT/SOUL penalties in the Game Boy Advanced version. Is this true?

I realize that this is quite an onslaught of questions, but I don't want to play halfway through the game only to be disappointed in the way I've done things. I would truly appreciate any help that you are willing to offer.