Yes in the navigators seat with Graham again. Nauli you didn't buy that car not to enter TW.

I believe you can enter TW with a car that meets TT regs.(must be able to because a lot don't meet CAMS regs)
Also the wheel regs for TT say plus or minus, so 17 are legal on your STI. I would check what tyre sizes are available and go 17 if you can get a wide enough tyre.