I have recently re-done the walls in my masterbath. I have a jetted tub that had carpet around it. I removed the carpet and found a plywood base. I would like to install floor heat and tile the floor, as well as tile the surround around the tub and part of the walls. Do I need to put cement board around the tub over the plywood? Can I use mastic and tile the walls (already installed moisture resistant drywall)? Do I need to put anything over the floor (plywood subfloor approximately 1 1/8") or can I thin-set my floor heat in place?

I would not use mastic since it will not be waterproof. The greenboard is acceptable in a damp location but not a wet one so hope you won't be splashing in that tub now. Use modified thinset, not plain thinset, to lay your tiles. Your subfloor is more than one layer of ply and should be good as is.