That depends on a few things. First, are you planning to use real or fake plants and are you planning on aquascaping the bottom?
I'll do these out of order sorry, the gouramis, you should stick with one male or a pair. You may want to consider Leeris, Pearl Gouramis as they are beautiful when fully grown. Regardless you're stuck with one male or a pair. If you weren't doing angles I'd suggest one of th pigmy gourami types.
Angles, 2-4 if you plan a large school of rainbows. Use some rocks in two areas to form territories. Flat garden stone from the plant nursery work well.
With the rainbows, that depends on what type due to size. You need to stick with something on the mid-large size because of the angles. I'd school them 8-12 at least. If you can get away with it, I'd go 14-18. Just make sure your filter is rated for at least twice the actual water capacity.
You did not say anything about bottom dwellers, the clean up crew. A nice group of 6-8 corys would work well or you could go with a few dwarf crayfish. I'm a crayfish fan, so you know what I would do.
