I just came into possession of a coral tank that's roughly 350 gallons and I want to turn it into a tilapia tank. Not sure how many fish can thrive in this environment. I'm a long ways off yet, still need to plumb, figure grow bed size, pump size etc.
You can fit at least 35 full grown tilapia in that environment (as long as you have enough of a bio filter to handle them all). Maybe more, depending on how you set up.