Please, PLEASE don't make the early access version Steam exclusive. I won't wishlist on Steam, and I literally *CAN'T* buy there if I want to actually be able to play the game I bought. So making sure the game is available somewhere else (like, for example, here, where the current demo build is already available) is going to be important if you want me to be able to support you.
I do get that Steam has some tools itch.io lacks, so it'll be understandable if you can't do a combined release for early access. If that ends up being the case, I hope you don't remain Steam exclusive forever on the full version of the game. Because, as mentioned, locking a game behind Steam is a guarantee that I'll never be willing or able to touch it. And that would be a shame because I've really enjoyed the demo.
In case you need the backstory:
Since 2019, Valve has known the Steam client is causing harm to users with several medical conditions (in my case, migraines, but it's also affecting some users with epilepsy as well as a few less severe conditions). Their response to feedback about the issue has ranged from negligent to abusive depending on how patient the customer is with the company. The more you're willing to keep trying to push for the most basic of competence in providing the service you've been paying them to provide, the more likely they are to go beyond being incompetent and into being actively abusive (including but not limited to conduct which violates privacy laws in most civilised countries and even some US states).