Once the fish are around 4 inches or so, you should be able to tell males from females rather easily. Males will be thicker bodied and although they don't have a very pronounced nuchal hump like some other species of geophagus, their head will be noticeably larger and thicker at the top. The males will also have longer trailers on all their fins. I have a colony of twelve or so that I've had for several years, so I will try and get some comparison photos today or tomorrow.
As for breeding, once they started, mine would breed every two or three weeks. I've had mine from about 1" or so since 2010 and they're still breeding regularly.