1. Don't know
2. Yes, taller shield, bar risers
3. Shure, why not
4. Check out the ST list at http://groups.yahoo.com/group/ST2_Owners
TONS of info on mods. Typically people get exhaust, then performance ECU, then start lightening things like clutch and flywheel.
5. Too many to list. It depends on the specific part you're looking for.