Very nice set up! I'm thinking I would just cover the whole ceiling in them. Not sure how I could suspend them but definitely could look into it.Yes, if in doubt something stronger that drywall. Much will depend on how close the joists are but we got a decent idea after an inch of sand in one area.
I doubt they will do much at all apart from internal HF damping and not needed to cover entirely.
Best to put in frames and suspend 2 inches away from ceiling and walls. Use acoustically transparent covering.
My second home studio control room: View attachment 108798