Well there are multiple ways tto avoid getting exp and to simply get AP from battles. Only exception is the end of the third disc, where you are forced to accept exp in three forced battles. There are multiple ways of doing this, one can for example soak all the exp with Zidane, leaving 7 outta 8 chars on lvl 1, or you can share it to keep many people at still very low level etc. I will be deciding on this much later tho.