It's not so much how many, but the size/ feeding habits of the fish you want. For example you could put like 80 chromis in there and be fine, but a fewer amount of a larger messy fish would be a problem. I'm looking at a 180 myself until I get a bigger house, and was thinking 3 tangs, some fairy/flasher wrasses maybe a leapord wrasse, a small mixed anthias school of like 7-9 fish. couple clowns, a bangaii cardinal. So you could do something similar, as long as you have good nutrient export.