re: Switching out tub faucet and shower head.

Shower head will be interchangeable with whatever. 1/2" npt connection is standard

The faucet spout will be the same 1/2" npt connection

Your tub trim kit will be dependant on the valve inside the wall. If you know it's Moen, definitely go back with that

Edit: If you don't know trim kit Mfg, take the old one off and take some pics of valve inside wall . You should be able to look online to figure out what it is (or post pic here for others to chime in)