If you want the thing to be remotely reliable - do yourself a favor and pick up a set of S6/S8/A8 NA exhast manifolds and just elbow off of that. Custom made tubular stuff tends to crack really quickly and doesn't give any real benefit.
No, if you feed with AN3 from a stock banjo. Maybe even AN4 can work as is.
Stock rods live just fine at 25+ psi on small peaky hybrids. You'll be fine with any power delivery with a big turbo (it's naturally smoother acting), as long as it's properly tuned (and fueled!) and doesn't knock. Talking gasoline ofc.
Twins = overkill, unless you go E85.
I don't like this.
Comes down to personal preference ofc, and you're free to do whatever as it's your car. But to me the whole idea of such build is to have a "sleeper", that can surprise everyone with sudden 700+hp.