Your account holds your profile, your books and your team. Teams exist from the start, even when you are the only member, so inviting an editor or reviewer later needs no move.
Two-factor sign-in: turn it on in Settings by scanning the QR code with any authenticator app. After that, signing in asks for a six-digit code as well as your password. You also get ten recovery codes: keep them away from your phone, and if you lose it, each signs you in once in its place. "New recovery codes" makes a fresh set whenever you need one.