There are quieter exhaust options and baffles, don't panic
That's one only you can decide really.
If the stock wheel style came in an 18" I think they would look a lot better and to be honest I don't mind them too much as a 17 but larger wheels do add a certain something, a decent quality 18 is you limit if you want to retain the handling. 19's are a compromise and can be made to handle OK but I wouldn't.
"OK" sums them up really, with decent pads they get the job done, the optional / standard larger ones are better though. Some J-Specs come with them.
Try both.
Don't worry too much about age but get the nicest car you can for the budget you have, it's all about being happy.
Yes.
Drive as many as you can, do your research and use your head - it's a great time to be in the market for a Supra, prices are silly these days so you should get a nice one.
Oh and import mileage - don't let that sway you, chances are it's been tampered with