You could fit a group of 5-6 juveniles in a tank that size, but large, full grown angels will need more room...you might fit a pair in that tank.
Angels are slow, delicate fish who prefer calm, slow moving currents, dense marginal plantings with swimming room in the middle, some driftwood and an amazon sword would make a nice center piece and spawning site.
They also prefer soft, slightly acidic water that is clear and well filtered.(an ac200-300) would be fine, just turn the flow down some. Temperature around 78-80F.
Substrate isnt really important as far as angels are concerned, but if you use live plants, go with flourite.
Feed them a quality staple flake food supplimented with frozen bloodworms and brineshrimp.
Good tank mates include all corydoras catfishes, ottos, bristlenose, hatchets, larger tetras, and smaller, less aggressive gouramis. Some cichlid species that would coexist fine with them include: Keyholes, kribs, rams, and apistos. But I wouldnt add these in a tank of only 30 gallons.
If it were my tank, I would just get a pair of half grown angels, 4 cory cats, a bristlenose, 5 ottos with maybe a small school(4) of lemon or black skirt tetras. But that would really be pushing your fish load to it's max.
