The offset varies, but most low offset wheels work well, from about 10-25mm Some of the AMG and other tuner wheels from back in the day were even lower offset (0mm!) PCD is 112mm

Temperature wise, it should stay at about 80-90 when warmed up. It sounds like your thermostat is duff. You might find that the car behaves fine after changing it, as when the engine is colder, it'll be running rich.

Fuel shouldn't be getting near the throttle body, you are probably seeing the residue of the blowby gases/oil collected in the throttle body/air meter.
If you want to clean it out, use some carb/brake cleaner and plenty of rags.

Make sure you aren't using the 'E' Setting on the gearbox, use 'S'. This doesn't mean sport, it means standard. E will never use first gear, whereas S will if you floor it. Other than that, the switch doesn't do anything else to the shift points etc.

Cheers,
Ben