lots of questions young grasshopper, lol sorry couldn't help myself. OK. The TT setup runs on a sequential setup where as one turbo works, then the secondary works after it. You can run them in a parallel system which is they both come on at once but very laggy. On which is better, a TT or single, it really depends on what your wanting to do with the car, I prefer a single, but a quick spooling turbo, it creates more power without as much lag off the line, which is optimal for running 1/4 mile runs. There really isn't a way to tell if a car is a single or twin turbo setup without looking unless it's a promod car with a big turbo sticking out of the hood. On a twin turbo setup, you can run up to 18psi safely and 21psi on race gas (ex. 116 octane) A stock supra turbo motor (2jz-gte) can produce in the range of 800-1000hp (with the supporting mods such as a fuel system, turbo, etc.) and that is on stock internals such as the pistons, rods, etc. If you have any other questions, feel free to ask on here, I'm not sure about the a/r sizes but I'm sure MKIV.com will have that information for you, if not I can get it out of my manuals and mail it to you if needed. Good luck on finding your car
Later