Before I go diving into this one I gotta ask, for all intents and purposes it is DONE in terms of available story correct? All that comes after this in later versions is general tweaks and polish?
Correct. There's extended content insofar as epilogues and alike in the Patreon version but as far as it being as a complete story with answers to the mystery and conclusion to the story, this version has all that.
The caveat though is this version is a little behind insofar as some revisions made in the Patreon version both for clarification and QoL in some scenes when it comes to explaining some of the central themes a bit better.