I got a turbo out of a Mazdaspeed 3 i'm thinking about doin something similar, the turbo was designed to run 1 Bar... The work you put in is awesome! are you using 1 bar of boost? Did you have any problems with the MegaSquirt? Was it easy enough to configure?
If you want tires buy em off Tire Rack and get them installed in Buffalo their dirt cheap! 114 ea for Direzza Z1 Star Spec... bring a girl along and say she went shopping, usually works at the boarder..