I would love to give you a fully qualified answer, but I don't have one.
We are also looking into newsletters, and we have thoughts on how to do it, but it is still in process. So this is just a couple of thoughts of our initial investigation on this matter. Maybe more is to come when we start implementing this solution the next couple of weeks.
One thing I think you need to be aware of, is that you need a subject-id for your customers. That will work fine for those of your customers that are already in your business, but those that are not, still needs a subject-id.
One way could be to actually create these customers in your system and another could be to give them a fake subject-id (like an encrypted e-mail-address as subject-id). These subject-id's will show up in your hub/customer-data, so you need a way to make them distinct from your real customers.
Also, you need a way to trigger the send-of-newsletter-process. You would probably need an event, and this event could be triggered somehow, maybe by a DMtask, which does require some un-logical setup.
Regards, Thomas