I always use 3 eggs for my omelettes, but as long as you balance it out with enough SuperFree (if you're doing EE), you can technically use as many as you like.
I usually use 3 eggs, one red onion, one red or yellow pepper, a handful of mushrooms and a handful of cherry tomatoes, plus my HExA of Cheese and a bit of salt and pepper :drool: Lovely!