Piecing a kit together can become difficult, if you can find a used kit that needs a turbo or just needs the turbo rebuilt youll be fine though. 6262 will spool up fine but its a little small, 64mm is a good middle ground. couplers wont cause boost loss but they can blow off if not tightened enough. check out alot of the turbo posts on here and on clubgp and it will answer alot of your questions.