[Sammus]

I think you should mainly look at jump design. Most tracks (even club tracks where I'm from) have very poor jump design. They all have symmetric launch/landings or have the ramps like flat so you just case out and wash off speed when you hit it. Another big problem is the landing is way too steep, so you have no hope of downsiding it. You need to get the curve right in the launch and have a longer flatter landing for any hope of downsiding it. You also need to be flexible moving the launch/landing because its likely after it's built the jumps will be too hard/easy to clear. This can also be compensated by adjusting the lip on the launch, or the overall size of it if you got it really wrong.

Also, you'll need good drainage, else the rain will just wash a lot of the smaller stuff away and youll be left with a hard track covered in ruts and stones. Not too bad for the true offroad feel, but depending on your design it could make it a lot harder :)