If you buy it on itch.io you will get a free steam key when it happens. :)
I haven't decided exactly when to launch it yet. Some of it will depend on how it evolves over the coming few months. My goal is to make it awesome enough to warrant raising the price, then launch it on Steam with a big bang of new content!
There could certainly be a free demo, but right now I am dedicating all my resources to improving the game for people who have bought it.