Hi Trigger,
Angels are a bit sensitive to high Nitrate levels, and prefer water to be on the soft side (roughly 2 - 8 degrees general hardness), but apart from that they don't require anything particularly special to thrive (only the obligatory zero Ammonia and Nitrite levels). As you are aware, they do prefer their own compary, so a small group of four or more would be best.
As for feeding, live or frozen small inverts are the best i.e. Daphnia , Bloodworm, Cyclops, Black Mosquito Larvae etc. along with the usual tropical flake.
Marc