This gourami, the Honey Gourami
, is fairly peaceful and better suited to smaller tanks. And your 3-foot 30g [which has the same dimensions as my 33g] is on the smaller side, but the length does give you a bit more option.
Always remember that fish for sale in stores are in almost every case going to be juvenile, and thus small in size. But they will grow, assuming they are fed properly and in the proper space. Fish grow continually, unlike us, and they develop internally and externally; in insufficient space the internal development which we cannot see will be deformed, often what we term stunted, while the external skeleton does not develop as fast. This is what happens when the tank is too small, or water changes are not regular.
When buying fish, you must always consider their adult size, and plant for that. Like the Red Tailed Shark
in that video: in stores they are about 2 inches or less, and look so cute, and people buy them. A few months later, the fish (if healthy and properly looked after) will be twice the size, and start getting territorial and very nasty, and it will continue to grow until it is 6 inches. It must have a 4-foot tank at minimum long before this, or it will not be properly developed, and its nastiness will be even worse--if it lives at all.
Always, always, always research any fish before you buy it. Make sure you now have the proper sized tank to house it when full grown. Make sure it is compatible in all respect: to your water parameters, tank environment, and other fish. If it fails any of these checks, do not buy it. It won't work, and the result will be sick fish, dying fish, frustration...and often leaving the hobby because you give up. This is a very common story. This is a hobby many people leave within a few months, and all because they did not research before buying. And sadly, one cannot be assured of the advice given by store staff in every situation.
Use our fish profiles. Most of the readily-seen fish are included. The data in the profiles comes from ichthyologists and biologists who know these fish well, and it is reliable and accurate. Back to the Honey Gourami
, our profile [you can click the shaded name for the profile] notes it can be kept in a small group in a 20g or larger tank, so a group of one male and 2 or 3 females would be perfect. It attains 2+ inches, so the little fish in the store are probably half this size now.
To your earlier question on other fish, now you've mentioned the Honey Gourami
. Tankmates must be quiet, sedate fish. Active swimmers--all the danio and barb species for instance--will not be suitable. The quieter rasbora species are good. And there are some tetra species, but be careful, as tetra can get fin nippy so avoid those species that may be inclined to nip [this is mentioned in the profiles]. And this is how you decide on fish, by researching all these aspects.
And the ancistrus should be fine in your tank and with these fish; you haven't given me the species name, and there are dozens of species in this genus, but those available in common stores will likely be a Bristlenose Pleco