Some insurance companies offer 'classic car' insurance on vehicles over 10 years, such as Lancaster Insurance. This will usually cost less than 'non classic car' insurance.
I got 2 decent quotes when I was getting my Supra, one was the official Supra Owners Club Insurer (Sky Insurance) and the other was Lancaster Insurance, Lancaster was cheaper on a classic car policy by £500 for me, thats with an agreed value for the car and like for like on the mods (just like what Sky offer).
The only downside is I have limited mileage (not a real problem in my case) and Im not covered to drive another persons car 3rd party.
With regards to MPG, I calculated mine at 12 but I have a fuel management system mapped a bit richer than normal. It costs around £70 to fill the tank.
To keep the Supra in tip top shape, you'll have to service it more regularly than I guess you service your current car (oil change around 3000 miles for example).
Reliability is great, and its one of the best looking cars on the road...not to mention the performance of the TT
The FAQ forums have some very useful info too.