Title explains it: I want to ask a question about maintaining branches of a single project and I'm not sure if it's on topic. If not, is there anywhere that it would be on topic?
Code Review requires code. If there is no code then there is nothing we can work off to improve, and so there's no way for us to help.
It should be noted that even if you have 'managing code' (via GNU make or Invoke), you may not get the answer you're looking for as we'll try to make that code better. But we may not necessarily make your management any better.