Yeah, there's a bit more clarification in the next version on the different worlds, but for replayability you get the option to either reset the level seeds for the Forest Map or replay with the current seeds. The different modes, are later phase additions, so they all currently feed into just the standard mode. That's clarified a bit better in the new version, though elements of combat are in Phase 2 which is next up. The additional modes will be in the free version as well, it'll just be worlds. Main reason is itch.io filesize limits. I struggled to get Forest into the file limit, so 3 more worlds will be impossible.
The plan for the additional worlds will be possibly a Steam release, rather than tying it to Patreon, though Patreon members will get a steam key as well, but it's not required for the full game!