I just wanted to give a little caution about "pairs" of angelfish, if you happen to have two males or two females (my case) they may very well beat up on each other. The alpha-female angel pretty regularly nips at the subordinate angel.
When they were small I tried to find a third, to help spread the aggression, but in my area there has been this drought of angels for such a long time, in any case now they're rather large and introducing a small one would be almost certain death for it.
With that as my experience I would say 1 or 3, and in a 30 gallon I think 3 is pushing it as a long term tank.
On the brighter side, my rams and angels never bother each other, nor do they bother the tetras. As was mentioned earlier, my rams would chase away the tetras on occasion, but I have never observed any actual violence.