I went looking through the wiki because I can't remember this ever being shown in canon, and I can't find it there either. I won't say we CAN'T do it, but AoE Boosts would be advanced tier spells rather than the basic tier. Likewise, just as Enchant spells are already advanced tier by default, making them AoE would turn them into WTF tier.
This part I'm not sure about. Apparently there's a spell that Lutecia uses to send Garyu off the battlefield to protect him from getting hurt, so I might make summons, or at least the Champion and Giant summons, similar to Barrier Jackets in that when damaged, they need time to recover. Not entirely sure how I'll play that, but any further information anyone can find on what the wiki calls "Repatriation" I'd appreciate.