This can be a big question, depending on your focus.
Geos are a fairly diverse group, even more so if you include relatives and similar fish, like Satanoperca. Within the Geophagus genus itself are a diversity of species and location variants. G. brasiliensis types are beefy and somewhat belligerent, many expect them to ultimately be reclassified as their own genus, hasn't happened yet. What people call "suriname types" are a number similar looking and behaving species of widely varying size, with varying color patterns, typically some combination of red to orange, green, blue, turquoise, and generally similar temperament and behavior, some more feisty than others between themselves or with other fish, but generally you'd keep them with milder species. Most are pairing cichlids, except steindachneri and its close relatives, which are harem breeders.
Then there are the Gymongeophagus, cool water fish, most need a cool down from their normal temps to simulate their winter, so no heaters needed.
Nearly all appreciate or need soft substrate like sand. Temps vary, most suriname types like mid or upper 70s to low 80s. pH varies, including among suriname types. Some do come from soft water, lower pH, but not all. Some come from neutral or higher pH, with no problem with a bit of moderate hardness. There are a good number you can keep in pH almost anywhere in the 7s.
Most like to be in groups as babies and juvies, quite often as adults they don't mind either way ime, especially breeding pairs-- excepting Steinys, as mentioned above.
Many will fit a 125, with some exceptions, some, like G. altifrons, should really should have larger tanks as adults. All of which leaves some questions imo. What's your water like, are you thinking of a species tank or a community, what other fish are you considering, etc.
