I bred about 30 different species, described and undescribed. In brief, I learned that their territories tend to be larger than our tanks, so they can't be crowded. Stress kills them. Females are more assertive and tend to dominate situations way more than the books admitted. Every species has to be approached as new, and what works for one doesn't automatically work for another. Water hardness is crucial, pH isn't. Body shape tells a story of their evolution, in most cases except for Venezuelan savannah/Llanos ones. Higher bodied Apistos tend to be less specialized in their needs. Some, like Apisto eunotus, are as easy to breed as any Cichlid. Others, no. Each species can have numerous colour and fin shape morphs, but commercial Apistos have gone into a breeding blender and that has been washed away. There are McDonald's style Apistos now.
What you see isn't accurate. I had Apistogramma gibbiceps from a clear water biotope, and they easily bred and raised fry in my 140ppm, pH 7.4 tap. I got some from a blackwater river, and their eggs died in my tanks, til I cut the water with snow melt, at which point they bred. Identical looking, but on their way to becoming separate. There was a lot of that. There are cryptic, unidentified species lurking in what we think we know.
I also learned it's hard to have a favourite Apisto. Even the ugly grey ones are interesting. They divide, loosely, into groups, and are a great window into speciation and diversity.
Tankwise? One pair per tank, no other Cichlid companions, if you want to keep them for more than six months. They're small, even if many are feisty.
And most importantly (and most unpopularly) if you like a species or morph, you can't count on the aquarium trade to resupply you when they die of old age. Either you breed it and keep at least 2 or 3 tanks to maintain it, or you may never see it again. Apistos go through the hobby and vanish, and the species we have available now are a fraction of what we could see in the past, if we went looking in specialty stores. And oh yes, they are an expensive hobby. I paid for mine by writing about them. They were popular in the past - not so much now.