3 psi on main before drop to 1/2"

The psi on the main Mobile Home Park side is 3

This is before the from to 1/2" pipe leading into my homes main.

The old pipe is galvanized, 3/4 to 1/2" I believe.

In repiping all the water lines to 2 baths 2 toilets 2 kitchen sinks & washer –
What would be the the best pipe size solution to get the most water pressure?
Thank you in advance.