If you plan on breeding angels, a pair will work. If you do get angels, they should not be the first fish in the tank whether cycled or not. Some good companions for the angels are Dwarf Gouramis. They are a very hardy fish and will add color to your tank. Also, if you get angelfish, the tank should be at least 18 inches tall and heavily planted. Hope the info helps!
Here's are some links for Angelfish and Dwarf Gouramis as well as compatability of different fish:
I think I heard once on Fish Lore that gouramis are not good companions for angels. Angels can bully gouramis if they're a breeding pair.
Besides, for 6 angels a 30G tank is WAY too small. Once a pair forms, you have to have a separate tank for it, or else they will fight the rest of the angles while trying to protect their eggs. Not a good idea to have a breeding pair mixed with other angles in one tank.
P.S. Please read my other comment in the other angelfish post.
120 gallons!!! You're so lucky So are you going to get 6 angels? Space-wise, they'll all have enough space for sure! But just watch in case a pair forms and becomes aggressive toward all other fish during breeding times. It's natural to happen.
Well, I know that a tank as large as 120 gallons, with a beautiful stand and canopy, plus the filtration system and all of decor, and whatever else that may apply - may cost as much as a couple of thousands of dollars. It really depends on what you're going for. It may be even more expensive if you're planning to have a densely planted 120G which would require expensive lighting system, plus CO2 generator if you'd like one. So ... how much are you going to pay for it? LOL! If it's for free, you're very lucky!