A 75 is a good starter tank for Nicaraguense, although in a couple years they would out grow it, unless you kept only a compatible pair.
Some live bearers as dither fish would help kept them comfortable.
I started with a group of about 8 juvies.
Once a pair formed and started spawning rituals, I removed the rest. The pair were very compatible and spawned many times.
They prefer hard water, a pH in the 8s, although mine did well in a pH of 7.8, mid to high 70s temps, Total hardness 250 ppm.
Males have spots in the dorsal and anal fins.
male above, female below
females not spotted, solid color, whole body more orange.
They lay non-adhessive eggs, mine liked PVC caps or caves for eggs and fry
Normal filtration is fine between 5 and 10 turnovers per hour, with average water movement,
they are omnivores so a basic pellet with an algae as part of the base ingredients works well.
The most important part for me was regular water changes to try and hold nitrate to below 15 ppm (my personal goal is < 10ppm).
Fry grow quickly
Mine were not hard on plants, (aquatic or terrestrial), so I would imagine in the sunny room in your photo, terrestrial plants such as pothos, or diefenbacia with roots dangling in the water, would grow well, as would hardy aquatics like Vallisneria provide cover, and help use up nutrients like nitrate.
I liked pool filter sand as substrate.
