Haven't strictly done proper motorsport but

for the d300, versatile and have loads of focal points.
Only motorsport I've done (heavily cropped) is with the tair 300 m42 manual lens... m42 links in the signature. Didn't turn out too bad.
D300 is the semi pro, well built. If you are on jpeg only you can get I think around 8 shots a second, and a camera that sounds like machine gun fire
On raw, its a bit slower
Since motorsport is not always close, you'd need at least a 300mm lens and probably a crop camera, so d7k, d300 (poss d90) would be my preference.
Lenses, I dunno. As long as possible with as low an f# as you can. Probably best to borrow a lens to see whether the focal distance gets you close enough, then find a lens of that mm but with better glass. Problem is that these are usually expensive...
Good luck
Oh and go n handle as many bodies as you can on the upper end... possibly a d2s might do the trick, still a crop but and old pro... Again if you can borrow it to try perhaps...?