i have about 8-10 types of gouramis in a 650 gallon with a single angel and they are all FINE, i have never once had a problem with anyone, just make sure you watch your angel when he matures (mine is only 2-3 inches big) because they might want to nible at the beautiful ifns!
the amount depends on the sixe of the ouramis, they range from 2 inches to 6 inches mainly, but some go to 12-24 inches long! plus what other fish int he tank with it? If no other top to middle swimmers, then i would say about 20 inches of gouramis
