I concur with
@Essjay . In a 5-foot long tank, you could have a nice group (my aim would be a group of 9, with three males) of Pearls (
Trichopodus leerii) so assuming this species I will offer the following, though this would all apply to most any species of anabantid. And with this large a tank, there are a few other gourami species available, though only one species whichever it is; I can suggest these if asked.
This fish occurs in still plant-thick waters and should only be housed in well-planted aquaria with minimal water movement from the filter. Floating plants are important as the species, like all gourami, spends much time near the surface, browsing plant leaves and dangling roots for food and most importantly, having to "breathe" air regularly [more on this below]. Floating plants also provide support for the bubblenest. Subdued lighting, partly achieved with floating plants, will calm the fish. It generally remains in the upper half of the aquarium.
In common with all the species in the suborder Anabantoidei, this fish possesses an auxiliary breathing organ called the labyrinth, named because of the maze-like arrangement of passages that allow the fish to extract oxygen from air taken in at the surface. The fish
must use this accessory method, because anabantids are obligate air breathers. This evolutionary development allows the fish to live in oxygen-poor muddy waters. To accommodate this, the aquarium must be kept covered to maintain warm moist air above the surface.
For the filter, I would not use an undergravel. I was "raised" on these, but have since come to recognize some serious issues, and in a tank this large, you do not want to be having to pull the substrate out or somehow get "under" it as the detritus/organics will rapidly accumulate. A good canister is your best option, as you want minimal flow but still a flow through the tank lengthwise.
Sand is your best option for substrate. Especially if cories are intended, they need this [a few others will likely disagree, but there is frankly no argument on this]. Dark is preferable to lighter, but anything other than white sand will be fine as far as colour. I use
Quikrete Play Sand, their dark grey mix, which is available in Home Depot and Lowe's (I see you are in the US). And this particular brand is the softest sand you can get, so ideal for fish and plants.
As for plants, floating are mandatory, and the best is Water Sprite,
Ceratopteris cornuta. Frogbit is another good floater, and then there is Water Lettuce (
Pistia stratiotes). These three are more "substantial," in that they have good root systems, and will cover the surface in short order if conditions are to their liking. Water Sprite is native to gourami habitats, and its regular production of adventitious plants on alternate fronds (it is a true fern) allows you to cull the plants easily and always have enough. Lower plants are up to you, but
Cryptocornye species, Java Fern, Java Moss and
Anubias are all lower light requiring and may be suitable. Nymphaea lotus is a "lily" that is planted in the substrate and in low light will usually send up primarily surface leaves; there is a red variety that is especially lovely in this type of aquascape. A substrate fertilizer tab like
Flourish Tabs is necessary. Or you could have lots of branches with fewer substrate plants.
Tankmates are not difficult to find; they must be OK with the warmth (Pearls have a range of 24-30C/75-86F and are probably better in the mid range, around 79-80F. Rasbora and tetras will provide the most options here, I'd be happy to discuss further if asked specifics. Many of the cories would find this temperature difficult, but
Corydoras sterbai, C. adolfoi, C. duplicareus are three that come to mind that are fine at but not over 80F, and these seem fairly easy to get these days.
