Most of the rift lake cichlids get too large to be properly kept in a 36g tank. They should be in groups so they can behave "naturally" and there just isn't room. However, there are some small species, like the shell dwellers if you want to stay with rift lake cichlids.
As for how many tropical fish can go into a 36g tank, it depends upon the fish species. There are many "dwarf" species, fish like Ember Tetra, Scarlet Badis, and many others that need to be in groups and you can have several of these in a 36g tank. You need to ensure the water parameters are suitable of course. Moving to slightly larger fish, some of the common tetra, Danio, rasbora, etc. can be housed in small groups in a 36g.
We have fish profiles, second tab from the left in the blue bar across the top of the page; if a fish name is shaded in posts, it means you can click on the name to see that fish profile. In the profile it mentions preferred water parameters, how many of the species should be kept, the minimum tank size, and other information.