You will have to go staggered, and even say so by the 17x9 and 17x10.5. Staggered just means different size wheels in the front and rear. As for the dish part, that is about preference, and does nothing for wheel performance, or fitment. The offset, backspacing, of the wheel will determine everything.
The 315s should fit. It is a pretty common tire now days on GTs. IF, and I say IF any modifications need to be made to make the 315s work, it would be flipping the quad shocks, or rolling the fenders. Flipping the quad shocks takes 1o minutes with the wheels off anyway. Rolling the fender is easy, if you are patient. I used a heat gun, and a cheap $10 kids baseball bat from Wal-Mart. I wrapped it with sports tape (the cloth stuff), and heated and rolled the bat back and forth on the fender lip until it rolled up just enough to be out of the way. You can rent a tool to do it at home (which is a lot easier), but you still need to use the heat gun. It helps soften the paint so it doesn't crack while you are rolling the fender lip.