Hi Welcome to the club!
Like any car, there are reliable, well maintained Supras, and some dogs! Best bet is to read through the buyers guide and make sure you follow all the points.
However you're asking about fuel economy, and cost of parts and servicing... you know this is going to be an expensive car to run, especially at 70 miles per day. I get about 250 miles to a tank (£70), but as it's a weekend car I probably drive it harder than you would be.
I have noticed parts are expensive compared to other jap cars, not sure why this is but with a bit of planning ahead you can get a good deal on parts from Traders on here.