Dunno if I'd consider #1 a "big" disadvantage.
Absolutely. We basically did exactly this in our games. Sponsored and Catches can be attached as a control for any powers, not just Magic, so long as it's thematic.
Example: "Samson"
(0) Sponsored: God of Abraham, Isaac, and Jacob
~ (+1) Catch: Nazirite (can't cut hair/shave, no booze/no grape products, no becoming impure with/touching corpses)
~~ (-6) Mythic Strength
Edited: to fix formatting issue/one typo
I don't really see the need to actually attach the Sponsorship to a power (or set of powers) unless you mean to indicate that you'd only allow taking Debt on rolls associated with that power (/those powers). Personally, I would just adjudicate that based on the table's shared understanding of the Aspect related to the character's relationship with their Sponsor.
