One thing I have found my choc gouramis like (almost need really) is good floating plants. I see your tank is well planted, which is great.
I have found my fish benefit from shorter lighting periods, slightly acidic water (i keep mine at 6.7-6.8) and whatever floating plants I have. I have Elodea cabomba and they have both done the job well. As regards pH - do your homework on what particular species you get. Find out what their wild habitat is and how they have been kept before they got to the fish shop.
I have also found chocs to be very sensitive to sudden brightening of lights at unexpected times. I once forgot to feed them when distracted by my sons in the bath! (they nearly flooded the place!) My lights are on a timer, and I went down 1-2 hours after lights out. When I put the light on the fish were very jumpy and looked a terrible colour, and didnt really take to food anyway. 24 hours later with additional plant cover and reduced lighting they looked better. This is something I wont do again.. they can always nibble on my plants if they are really hungry
Feeding wise I give mine a combination of frozen live food and flake. I found they like baby brine shrimp and daphnia. I think live food has been a real good thing for them, making them much stronger and improving their colour a lot.
As regards tank mates, tey seem ok, but I never trust tetras when it comes to not nipping. Chocs are very slow swimmers (they can zoom if startled, but this is the exception) and are stationary for prolonged periods. They are a very tempting sight. I would observe closely when introduced into the tank.
Also bear in mind, my experience comes from keeping Vaillants chocolate gourami, (Sphaerichthys vaillanti) which may be different from the type you are considering.
One final note, there is a reason why most LFS dont keep them. They cant keep them alive long enough to sell them.... they really are a most sensitive fish. Beautiful, but sensitive... good luck.
ps... i forgot to say. sexing depends on what species... for my particular choc, the female is more brightly coloured than the male, and is slightly larger (before anyone asks.. yes female is brighter) Some are nigh on impossible to sex