I have twice maintained Chocolate Gourami, the first back in the late 1980's when I lost them to Velvet, and the second time a few years ago when they spawned several times and I managed to raise some fry. Sadly the whole group was wiped out with a pathogen, but this leads me into some advice starting with disease.
This fish is very sensitive to water conditions, and highly susceptible to disease. Water must be very soft (hardness below 5 dGH) and acidic (pH 4 to 6.5 but preferably below 6.0), and warm with the temperature 26-31C/79-88F. In hard or basic water the fish will be stressed; it is very prone to skin parasites in unsuitable water parameters or conditions. Regular partial water changes maintaining water quality stability are essential. Fluctuations in water parameters or quality often lead to skin parasites, bacteria, and fungus.
These conditions immediately limit tankmates, as many cannot tolerate such warm water, but the second time I kept the temperature around 80F and with this the quieter rasbora (Trigonstigma hengeli, T. espei) work, and I also had a group of pygmy sparkling gourami, and they too spawned regularly. This was a 70g tank, and I would stay with the Chocolate Gourami and perhaps some rasbora in smaller tanks.
It is best in a small group, as it is very social and the interactions of males is well worth observing. The tank space will determine the maximum, but I had a group of six which just happened to include male/female. The tank must be thickly planted, very thick. This fish does not need swimming room, preferring to cruise very slowly among wood branches and vegetation, fairly close to the surface. The tank must be covered so the air remains warm, as being an anabantid they regularly take in air and if this is cooler than the water it can lead to health problems. Wisteria (Hygrophila difformis) is an excellent plant; stems can be planted and allowed to grow up to the surface, and then along the surface (lower leaves may die off though when it grows along the surface), or it can be kept trimmed to surface height and other floating plants like Water Sprite (Ceratopteris cornuta) used for floating plants. Thick planting is very important, and lots of wood. Dried leaves (oak, beech, maple) on the substrate would further increase tannins and help prevent skin issues.
Thick plants will also provide more shade, which is essential. This fish occurs in heavily shaded forests and peat swamps. You could have just floating plants like the Water Sprite, which will easily grow over the entire surface, keeping the lower portion of the tank in shade, and just use branches, chunks of wood and leaves as lower decor. Substrate can be smooth sand or fine gravel, with sand preferable. The filter should be very slow; a dual sponge filter works fine, or a slow-flow canister filter. You need good filtration but scarcely any actual water movement.
There are presently four recognized species in the genus. The most common is Sphaerichthys osphromenoides, followed by Sphaerichthys selatanensis which is nearly identical in appearance. S. selatanensis has a horizontal creamy-white band mid-line on the body in addition to the vertical bands, whereas S. osphromenoides has no horizontal band. The third species S. vaillanti is sometimes seen, but the fourth S. acrostoma is very rare in the hobby.
Males of S. osphromenoides have a light (creamy white) edge to the dorsal and anal fins, and females have a dark spot on the caudal fin; males may have a reddish-brown hue over the body. Unlike many of the anabantids that are bubblenest spawners, this species is a maternal mouthbrooder. The pair circle each other and the eggs are laid on the substrate in a shallow depression, fertilized, then immediately picked up by the female and retained in her bucal cavity for up to 14 days before the fry are released. With a thick cover of floating plants, several fry will usually survive. They will find microscopic food among the plants, and the dried leaves mentioned previously will provide more as infusoria. Finely powdered flake food will be taken.
Hope this helps. A fascinating fish that is worth the effort and care.
Byron.