#12 wire wire will be OK. I would run #12 uf w/ground from the well to the pressure switch. I would run #12 w/ground Submersable wire from the pump to the top of the well. I recommend using a Pside-Kick http://www.cyclestopvalves.com/products.html as it includes everything that you will need. The Pside-Kick will keep the pump from cycling and give you city like constant pressure.