I have no idea how identity works in WN/Marmot. I want to find others' identities starting with my npub's follows lists. I assumed I'd have to share my WN npub - my WN identity - on my nostr profiles so others can chat me.

Yeah, I'd love to have a way to see which npubs are on marmot, we'll implement that in the future. No, you just need to share your regular npub, a client can then look up your keypackage and encrypt messages there.