1)Not sure why it doesn't, possibly b/c it's not the same chassis. Your better off finding an actual conversion.
2)The 3 you just listed, from what i have read, are the best out right now. Greddy is STILL in the process of releasing a 50 state legal turbo for the S14. But i think most ppl have had luck with the Fmax stage 2 turbo. Do a search on this one, there are plenty of topics.
3)Not sure, i would though...thats what the aftermarket is there for, to release products that nissan hasn't to better improve your engine's performance.
4)Yes
5)No one makes a rear end conversion that i know of, or we would certainly see more out now. I would emagine you would need the tail lights, trunk, rear fenders, and rear bumper. but anythings is possible with $$$ and a good body shop.
I dont know much, this info is just what came up in the search i did.