Question on New Shower Install Pipe Sizing

I am currently remodeling my bathroom downstairs (same floor as the water supply entry to the house).

I want to install a Moen U thermostatic valve with (two) 1/2" inputs and (two) 1/2" outputs.

I plan to use these to install a rain shower in the ceiling and a standard showerhead on the wall. with the plan of using both simultaneously.

Question for you experts… my main line into the house is 3/4" that necks up to 1" after the water meter (all copper right now) and for some reason goes down to 1/2" when it hits the ceiling of the utility room.

that half inch feeds everything in the house. 2 bathrooms, kitchen, wet bar, urinal off of my mancave (Don't ask lol), and 2 hose connections. spread across 2 floors.

I want to get enough pressure going to the downstairs shower to supply those 2 shower heads with enough pressure to take a good shower.

If I increase my mainline to 1" (or 3/4"???) pex from where the 1 inch copper currently ends, and run 1/2" cold line to the bathroom (about 15-18 feet, give or take), and 1/2" line to the hot water tank (and 1/2" line from the hot water tank). will that give me the pressure I want?

or am I better off running the 1" (or 3/4") cold supply pipe all the way to the valve, reducing to 1/2" there, and connecting into the moen U valve? and similarly run 1" or 3/4" from cold supply to hot water tank, then 1" or 3/4" from the hot water tank to the hot side of the shower valve?

bathroom is about 75% gutted (everything but the floor and ceiling is out) so now is the time to upsize the supply to the bathroom if that is what it will take.

Thanks for everyone's input!