Hey Lucas!! Sure thing! I originally planned Adventure Below as a short follow-up free expansion to Adventure Begins instead of characters, but the popular demand for sprites and interior tiles made me think again about the release plan! Adventure Below will have the same pattern (general tiles -> character expansion -> more expansions made by following feedback).
In short: Adventure Below, being its own thing, will be a separate itch.io project (of course bundles with Begins will be there) and a patreon monthly reward. :'>