Giant Danios are too big and active in my opinion for this tank. And I've never owned a Rainbow Shark but I know that Red-Tailed Black Sharks can get quite aggressive. The Opalines will be fine as long as you only have one male. I would add a nice big shoal of something like Puntius Pentazona to keep up the Asian theme you have going. Or maybe Rhombo Barbs, both of which look similar to Tiger Barbs but aren't as aggressive. What I would do is this:
4 Opaline Gouramis
1 Rainbow Shark
10 - 15 Puntius Pentazona/'Puntius' Rhomboocellatus
OR
10 - 13 Puntius Tetrazona [although they may have problems with Gourami]
TekFish