I am happy you enjoyed the game :)
While the final game will have more metroidvania elements than the demo, it will be executed in a manner thats different to most other games of the genre...I don't want to spoil too much but yeah there's definitely gating that can be overcome but you aren't going to be an overpowered force of death by the endgame! As for your questions:
1. I want to release it on the Switch and PS4, but if this were to happen it would probably still be a whiles away as I want to release some free DLC on the pc version first as well. I have no idea what the porting job will involve either, but since I am using Unity I hope it isn't too much of a headache.
2. The launch price will be 14.99 USD
3. No multiplayer...it's one of those things I have always thought of adding down the line but it definitely won't be a straight forward task as there's a lot of code which takes the assumption that there's only one player. If the game gets popular enough to justify it though I will add it as free dlc at some point.