pex expansion

Hello everyone. I am remodeling my jetted tub/shower down to the studs. I currently have 15 year old 1/2 CPVC pipes. I will be installing a 2.5 gpm shower head with a 2.5 gpm shower wand to a Delta 3-way multi valve. The shower valve is supposed to be rated at 5.3 gpm at 40 psi, 6.5 gpm at 60...