You could run 1/2" for hot side, lav and shower
I would run 3/4" for the cold side, toilet, lav and shower. Each fixture would get a 1/2" branch.
I am adding a 2nd bathroom on the top floor of my house and I'm wondering what size PEX to run for the supply lines. I will be tapping into 3/4" galvanized Pipe right after the water heater. The total pipe length will end up being 30-50'. I'll be installing a toilet, sink, and shower.
How far from the fixtures should the branches start?
you would run the main 1/2" hot and 3/4" cold all the way to the bathroom, and branch off for the first fixture, then the next, then the next