1. no 2.25 in piping is fine. i dont see why that piping wouldnt be good as long as its bead rolled at the tip so your couplers don't blow off..
2.450cc just in case you turn boost up or whatever
3.yes that's the same setup i have works great going strong on 7 months
4. turbo timer would be more convenient than waiting in the car for the turbo to get cooled down. so yes.
5.i think so, maybe some other turbo heads will chime in.

what are you tuning your car with?