2008 Speed 3 Daily/autocrossing setup

Hello, I recently bought a Mazdaspeed 3 and would like to take my car autocrossing. I have some high performance all-seasons on the car and would like to get and actual summer tire and some new wheels. I am thinking of trying to get wider tires (235s, maybe 245s) to get more grip. What setup can I run to achieve this on stock suspension without any bodywork (rolling or cutting fenders)? I am thinking of moving down to 17 inch wheels for my summer tires. What I have seen so far, I should be able to run 17x8s.

Edit: I am also unsure of offset, I have seen most people with 17x8s run +45s.