i am basically your SAME build. I ride *[rode]* a 2006 CRF 250R. Great bike forgiving, but lots of power for a track, you glide over EVERYTHING! search sero901 on youtube, there is a vid of that bike, AWESOME!!!!!!
They are not cheap to maintian, but i am 16, work 6h/w and maintained it, with no financial strain. FUNFUNFUNFUN!!
good luck! (trail bikes are not meant for track, slower, lack power, cheap to maintiain. not a track bike) (racebikes are good on both, basically over kill for trail, but suspension ajusts in seconds so it is good!)