1 A&B) Any V brake will work. The cheapest one will still lock that wheel right up.
2) You'll want a DH strong stem, unless you have a good dental plan
3) Get a frame that fits. You shouldn't be sitting down anyway.
4 A&B) 3 piece cranks with a splined spindle. You need a titanium spindle like Beerman needs a tutu.
5) As long as your bars are cro-mo, they'll do the job
6) Use regular tubes, learn to fix a flat.