Very luck with that crash! Sometimes, I believe in fate, and on that odd day a seatbelt isn't worn and a crash happens, you servive because of it. Seatbelts save lives. fate saved my life once not wearing one.
It could be the thermostat housing, itself or it could be a seal around the sensors that fit in it. If you remove the yellow plug and bridge 2 opposing terminals, the fans should kick in. The leak could also be the seal between the stat housing and head.
There is an adjustment screw on the throttle body, adjust that screw when warm to get the correct idle. It may idle higher when cold, but what vr doesn't?
Both really, but more so turbo. If you run a large enough exhaust housing on a turbo then you'll boost later in the rev range, almost eliminating the sudden mid rev range 'kick' you'd get with a small housing, so more like a supercharger.