1) Pistons, header, exhaust, maybe an intake if you can find one. Everything else would be custom, custom Crower rods, reground cams, etc.
2) You can turbocharge any engine. You'd just need custom parts to do it.
3) 6-8 psi should be ok when tuned.
4) Rods. Then sleeves, pistons, head studs, etc. depending on how high he wants to bost.
5) Any B-series would be better, ideally one of 1.8l or more (this means no B16A's, B16B's, or B17A's)
6) An H-series would be beautiful.
6.5) Good luck stuffing one of those in an 88-91. Talk about full custom installs!
7) The best engine would be an H22A because they displace a large volume and have plenty of aftermarket parts availible. It'll be hell to swap into that car, though.
8)With an aftermaket suspension, it should be peachy. Handling problems in Civics with H-series engines tend to be exaggerated.
9) The B20A will make your 200-250 with a custom turbo kit, but for 300-350 you should trash it and go for a custom swap.

In the end, an 88-91 Prelude is a pretty bad choice for mega-power builds because there is so little in the way of an aftermarket for them. Keep in mind that engine has a 1.51 rod/stroke ratio, that's horrible, and why it has issues. Honda should have never made that engine IMHO.