Houston, we have a problem!
You should not use PEX, or CPVC, for the tube leading down to the tub spout. Because of the small ID, when you are running water to the tub, you may well have some water dribbling out of the SHOWER HEAD. Some brands mention this in the installation instructions, some don't, but expect trouble. You should either do that drop in copper, or bump it up to 3/4 CPVC.