Honestly, if you wanted you could make manual patches available here or elsewhere for the Steam version with each finalized bit of new content while still updating the project here. Sort of like how JP ero games release versions with significantly less explicit content there and advertise the existence of an external patch that adds the missing content back in.
That way, you could get continual feedback on the new CGs and routes here while releasing the final versions of those revisions to Steam players via a community post or announcement at each milestone. That way you can tinker with the game publically without there being a significant discrepency between versions.