As I note you recently joined, may I first welcome you to Tropical Fish Keeping forum.
We have a section entitled "Tropical Fish Profiles" accessibly from the second tab from the left in the blue bar across the top of the page. Many fish and plants are included. The Opaline Gourami is included, under the common name Blue Gourami or the scientific Trichopodus trichopterus. When a fish name appears in posts exactly as in the profiles, whether common or scientific, it is shaded as the afore-mentioned names are, and you can access that profile by clicking on the name. This species has several common names, we can only choose one, and "Blue" is the more prevalent in the literature.
In the profile it mentions that this species should be kept in a pair (male/female) unless the tank is much larger than a 29g. Males are territorial, and can be very aggressive. However, a male and two females would work.
As for tankmates, all gourami are quiet, sedate fish (notwithstanding their territorial aggressiveness to each other) so companion fish should not be active or aggressive. The medium/larger rasbora work well, the quieter medium-sized barbs such as the Black Ruby Barb, and substrate fish such as the smaller loaches (in a 29g the under-4 inch species) and some catfish. Plants, including floating, would be appreciated by this fish.