What kind of pleco do you have, may I ask? If you don't know and can get a picture, I'm sure someone could ID it for you.
What kind of danios do you have? Again, a picture would help someone to ID it if you don't know.
The reason I ask is zebra danios, which are common for people to get, actually prefer a bit cooler temperature than the tropical fish you are looking at for centerpieces.
They also would really do much better in a longer tank because of how active they are. Most say 4 ft, and others say you can get away with 3. Also should be kept in groups of 6+.
I'd say an angelfish wouldn't be a good fit for this size tank, they get quite large and need a tall tank, though I think the height of yours is just about right.
Opaline gourami can get up to 6", and apparently should be kept in no less than a tank with the dimensions of 36"x12"x12". (Taken from seriouslyfish)
Going on all that..I'd say honey gourami would be the best fit. They're quite lovely and stay a reasonable size.
I hope I didn't come off as harsh in any way, I don't mean to. Just wanted to give you some stuff to think about.