I agree with ML on the cadenza idea that it should all be within the bounds of what the natural trumpet can do. I've also been very surprisewd how little a good amount of (american) trumpet players know about the natural trumpet's abilities (limitations?). I know a ton of players...good ones...that have never played or heard a natural trumpet live. Aside from solo rep and ornamenting, this has big implications when it comes to a lot of the symphonic rep as well. I'm told that in England it's part of standard conservatory education. Seems like it's lacking on this side of the pond.