2-3 times a week is plenty for adults. As far as how much to feed them, thats hard to say, you kind of need to feel that out, most of mine eat 10-12 cricks a feeding and if its mealies, more then that, little pigs lol. Just be careful because you dont want to overfeed them.
I feed my adults mostly superworms and mealworms, and I try to keep their dishes full at all times. If you're feeding crickets, I'd only let them have as many as they'll consume in an hour or so. Surplus crickets running loose in the cage can annoy the crap out of a gecko.