1. Flare and Holy are both elemental spells that hit a single target, while Ultima is a non-elemental magic that hits all enemies. All three spells can dish out 10k damage when used by a strong magic user, and on the right enemies, but Ultima is far superior because it can't be absorbed (due to it not being elemental) or reflected.

2. I do my training in the Omega Ruins after a certain point.