It's a class thing. Car is "street legal" even without the street wheels. I drive it on the street with radials and skinnies.
But - yes. some classes require a full interior, or X miles without filling up or fucking with the engine bay.
Street car
Decide on what you want to do and what you can afford before you start doing shit.
If you want a good-looking daily, do that. Don't start fucking with the engine. If you want to build a drag car, know it's going to cost 100k, and don't cut corners. Also, make sure you have enough...
I'm not sure who Supra Gremlin is, with that time, I assume it's Rob. That's a solid time. ETS is a great kit, and if you want that you should go with it. The P2uned Kit is battle tested and has won more races than anyone else.
Lots of PTE Turbos here, Lots of Xona, Lots of Garrett.
The downpipe was not the problem. You can drive around without a downpipe for 100k miles and no tune and not cause any damage. In fact, most people do this (or with a JB4).
I'm unsure what 'Reset ECU' actually does- that might have caused some trouble. I'd put the factory downpipe back on it...
It'll come to 220°F nearly instantly. B58s are very good at heat management (at least from engine temp standpoint.. IATs.. not so much). 4 of 7 bars is right where it should be.
If you want the exact temp, you can get that from Ecutek or any other OBD reader.