Does the 1/8 scale Top-Flite radial engine fit in this plane?
Yes!
Has anyone used the cockpit kit for this plane?
If you do a RCU search on this model you will find a thread by an Italian fellow who did put the cockpit kit into his.
I would like to put a tail wheel retract in it, which one do I buy? and do I need to run 2 retract servos and "y" them?
The Robart tailwheel is the only one I know of. I bought it for mine. And yes, two servos with a Y harness.
Should I use a Saito 100 or 120?
More power is always a viable option. And you will end up needing noseweight anyway for CG issues so it might was well be in the form of an engine.
Where is a good website to find nose art for the P-47, the ones I find are mostly P-51's?
Dunno. Sorry I can't help you here. I make my own.
Where can I get bombs for the wings?
Hobby Lobby.