That's ridiculous, I had a little play with a corsa redtop one night, fast little feckers, funny how it's still registered as a 1.0 12v tho...
Good route to go down if you want a cheap track car, a redtop is only £200 so really you just gotta get it fitted properly and your off.
As for a remap, who taught you that? It's actually the opposite if you get it done properly. TDI's only smoke because the fuel delivery is the same when the turbo is spooling up as to when it's boosting full, causing the smoke until the turbo kicks in.
A remap will give you more power but also better spooling. (Even more so since i've got a decat) A bigger turbo however, longer spooling, more smoke.
As for the tyres, I got 2x 225/40/18's for £86 delivered, good price I thought.