I'm pretty sure the angels could live in there for a few months. There will only bee dwarf hair grass and some java fern. I think 10 neon tetras would be good for a school, a friend of mine is having a breeding pair in a 15g high. All angels don't grow the same size, i'm planing on getting silver or gold angels. But once they get big, i'll be sure to return them back to the lps for another pair or so.
I do agree with you guys that angels intend to get huge, but it should be okay for a pair in a 20g high.
I would get a pair of rams but they are too sensitive to water conditions and I can't risk loosing $20/ pair.
Edit: Oh by the way, I will be saving up for a 29g once I get rid of all my smaller tanks and sell some of my plants.