I currently have 3 angelfish (did have 6) and the only thing I would suggest is, if you do decide to get a second one later on make sure they are exactly the same size, if one is just a little smaller the big one will pick on it. Which means no food for the little guy and the next thing you know he's floating in the tank.
I also noticed they are vary sensitive to changing water parameters, I would suggest doing water changes in small increments, and avoid changing 50+% of the water at one time
And they only seem to fight with each other, I have a gobi, rams and mollies that are all half the size of the angels and they never bother each other
And lastly avoid getting a breed that is known to be small and putting with a breed that is known to grow large, in most cases death will occur
Sorry for the long message and hope that helps