I think that technically you can. But I do think it is against the AdWords TOS. May I ask why you want an "extra" account?
You can have an account for each site you have. And then you can manage all of them via one "Master" account.
Never heard of this. Can you explain exactly how to set this up? And possibly the benefits of setting up your account this way? Thanks.
So long as you don't mind logging in twice to see all your campaigns and also don't mind not being able to consolidate the data it is fine. I don't think there is any restriction for the domain too since i know someone who has different accounts for promoting the same website/domain.