some people may disagree, but here's my two cents:
it'll be difficult to find a frame that you can upgrade at a low price range. definitely go for a hardtail. check out Trek's line of hardtails. the frames from the 4000 series, I THINK are the same as the 6000's, and the 6000's aren't bad.
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i wouldn't use clipless for stunts. if you need to dismount (i.e. you wipe out), you'll have a problem if you're clicked in tight. i ride with clipless. i prefer clipless over platforms 'cause my feet don't slip off the pedals. however, i really don't feel comfortable going airborne with them on. everything else is cool, though. I wouldn't be too comfortable riding skinnies over 6ft, though, either
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i'm in a bad mood too
. i'm sick from stress... hopefully pizza will cheer me up
.
have fun!