For the login workflow.
1) if a user creates a NEW account using the Steam login, they must login using Steam every time, or request a password reset using their email to initialize a login via the standard IPS login method. When signing in through Steam, the API doesn't give me the users username, password, or email address. When setting up the account, IPS only asks for a username and email and the password is left empty so the only way in is through Steam authorization.
2) If an existing user links their Steam account to their forum account via Account Settings, they will be able to login using EITHER method, Steam or the normal IPS account login they've already been using.
Steam doesn't 'take over' the account.