Hi Andrey,

let me have a think about that one.

Of the top of my head, I would think that – rather than reinventing the wheel – one could add/create another user role (let’s say customer) to the existing ones like subscriber, admin , editor etc and give people the option to become a member of that group/role when ordering .
After that , you can use one of the many mail/newsletter plugins to send your marketing etc…

anyway, let me have think about all you mentioned above.
Please give me a day or two though as I’m in the middle of some other things right now

thanks

Olly