Did any water readings change with the angel addition? Even if the nitrate went up only to 10ppm, I'd wait another week or so. Even better, consider a QT tank for new additions. That way you've always got a built in 3 week gap between additions. If the 'trates are at or very near zero, maybe the clowns will work. Get a small pair IMO
I'd consider another 30 - 40 lbs of rock before you add too much more anyway. Ensure it's fully cured (either before or after you buy it ) in there. Then, as the tank really stabilizes, you can concentrate on a larger cleaning crew - like 15 or 20 hermits, 10 snails and a couple of shrimp maybe. And fish. I'm concerned you're not stable enuf yet for the angel. Clowns can be a lot more hardy during this period as you set up. Still, 4 or 5 hermits and 2-3 small snails might not be bad right now, but watch your water levels.
I know its hard, but you gotta go slow.