At first glance, I don't like the armor idea very much because the best way to play would be to always have at least one character using it at all times, even if it have low stats. I can see how this could be a solution for allowing the player to power level the weaker characters though. Maybe it could work if I make it into a single unique item that you can get if you complete some kind of endeavor, I'll put some thought on it.
The EXP item sounds quite interesting. I think it would fit well if it's some kind of rare consumable that only bosses will drop. Maybe every boss drops one of those so you can choose which character will consume it. Sounds nice.
I also want to think of another use for the items you can gather using tools. For now they are used only for concoctions, which is exclusive to Apothecary. Just not sure how, yet.