I have a 97 2.5 GT

I am not new to turbos and turboing N/A cars, although I really know nothing about subarus.

What happens when the stock ECU sees boost? Is this a problem? Can I swap to something like a WRX ECU if I upgrade injectors and stuff like that?

I have the DOHC heads. Will these heads bolt onto something like an EJ20T or EJ22T bottem end?

Does the EJ25 have a knock sensor built in?

Will something like a WRX or STI tranny bolt up somewhat easily? If so do I need the rear diff also?

Thanks for your time.