1. Yes, a 275/40/17 Nitto Drag will fit fine on the 17x8 stock wheel. I have this combo, in addition to my Cobra R wheels. Slight buldge, no issues with the Nitto's.
2. O/r pipe...BBK, Magnaflow...a bunch of companies. Are you looking for an H or X design? Do you want a matching catback?
3. After gears, I did a chip because of other mods anyway. I "believe" but am not sure, that you can buy a calibration module to compensate for the gear change. All my buddy's and I have chips, so I can't help further than that.