For me breeding projects are tricky, because it isnt only about getting the fish to spawn and raise healthy babies, but do you have an outlet for these babies? Will someone buy them, if not, do you have a tank to keep them in? I have my bolivian rams and while they spawn and I could raise the fish, they wouldnt sell and I cant keep them.
You can breed fish you could add to your larger tank to increase shoals of fish you have, but I am guessing you have softwater fish.
You can have fish that pairs up, breeds but ends up killing its offspring, which could work but it is a bit devastating and cruel.
You can have a sulawesi tank, tylomelania snails, shrimp..
You can keep any of the pseudomugil, see their interaction, they even breed for me on their own and I didnt have to do much to have some fry survive at some point. And they are very lovely fish.
You can aim at breeding and returning some special rare wild livebearers, depends on where you are from and if you have any clubs nearby, here people keep Xiphophorus xiphidium and ticos and others for example. They also present nice challenges
You could do a nano fish tank, or smaller calm fish that wouldnt do well in a community, and with your harder water and larger ph they wont breed. Or turn it into a brakish tank and play around with some gobies. So many choices
