"Can I buy the game in advance?"
Yes. If you buy the game here on itch.io, and pay $10 or more for it, you will get the final game for free. Think of it as a pre-order. I'm expecting the 1.0 version to cost $15 and be released in Feb/Apr 2018.
There's also another way to support development. Space Bob is not my first game. My first one was NeonXSZ, and you can buy that on Steam. It's a very different game, that took 4 years to make, but if you like the look of it you can buy that one to help support development of Space Bob.