Are you a citizen? Because if not, the answer to all of this is "whatever the hell border patrol wants". As far as I know, you absolutely could be asked for your bank account password. You wouldn't be, because any agent asking would probably be fired to avoid a media circus, but it's not actually against any rule. Border patrol discretion for non-citizens is almost absolute.

If you are a citizen, it's not clear that anything at all can be demanded, even logging into an account already on the device. It just hasn't been put to an unambiguous court challenge.