This is a
boat not a house. You do not need to have a flow rate of five gallons a minute. I used 3/8 pex which works great. Hot
water in half the time of 1/2 inch and if the flow rate slows down when wide open then my tank does not empty as fast. My house is also plumbed with pex. I use the home run system where each fitting gets its own line back to a master manifold so there is not a pressure drop when a second fixture is opened. 3/8 is easier to bend, cheaper and helps control
water usage. I have used a manifold with all the valves at the pump/bladder tank so no elbows or T s, every fixture has its own pex line and valve at the manifold.