Using Larger Pipe than Water Inlet
I would run the line to the manifold in 3/4" and then the branch circuits in 1/2" like you said.  The cost increase is minimal and as long as you have the room for the extra 1/4" of pipe width, you won't second guess yourself.  If you put in the 1/2" and they upsize you main in a year, you're going to wish you had installed the larger diameter.

Yes, you want more than 0 psi at the point of use.  Most faucet manufacturers will say you need ~30 psi minimum for proper operation of the fixture.