I usually run 3 classes, and pick the 3rd between 2 vehicles. Last weekend I ran 4 classes since it was a bigger trophy race with over 100 entries...Yeah, I won't do that again!!
2-3 clases...No more.....If your still new, stick to 1-2, and get proficient. And I suggest not switching between 2wd and 4wd..It's hard to make the switch and not mess up one or the other.