On crowdfunding campaigns, it's normal to sell what doesn't exist yet. That's the whole POINT of crowdfunding, really. So us offering features that don't yet exist such as deluxe skins fit right in on Fig. But on Steam Early Access, it seems a bit weird to sell a base game and also a deluxe option with nothing different at all right now, that might someday have other content. So there will only be the most minimal option available (which has everything in-game that we currently have to offer at a reasonable level of polish), plus the soundtrack as a separate product in Steam.
To contribute more, the best way is really through Patreon.