What is the footprint on this tank? I would personally stay away from angelfish for this tank as it is likely too small. They really need something larger, in the 55-75 gallon range as they are large as adults and are often quite territorial.
Dwarf gouramis can be tricky. The males can be pretty confrontational, and I would say four would be fine if it was 1 male and 3 females, but finding female dwarf gouramis is almost impossible in my area (not sure how it is elsewhere). With 4 males, make sure the tank is either heavily planted or has plenty of places to hide. You may still be looking at stress and bullying with these guys and you may eventually only have one.
Bottom dwellers are always fun, just remember many of them are shoaling species and need to be kept in groups.