Hi
Depends what kind of service you mean, and who does it. Most things you can do yourself; Oil and Filter changes are obviously the most regular maintainance job and cost me say £40 ever 5000miles. Other stuff is so few and far between I wouldn't worry about. Cambelt need changing every 5 years or 60,000 miles. Brakes and tyres depends on how you drive.
Say 18 to 20mpg for a TT and 20 to 24mpg for an NA (Unless your name is BlitzSupra in which case you will claim 36mpg)
Nothing much, no regular problems. Emissions might be an issue if you've removed the cats. Can't think of owt else.
Big, 300+bhp, RWD, yeah they're quite hard on rear tyres. You should be able to get like 10,000 miles from decent quality rubber. 20,000 is very possible if you do a lot of motorway driving. However, if the car has been lowered without the geometry being redone it may well destroy tyres with uneven wear.