Ideas on how to make a membership driven newsletter

We have a 100 day email newsletter we sell. Im trying to figure out if there is a way to do this via someone buying the package on our site via marketpress, and then it signing them up for the mailchimp newsletter I have.

Is it possible to have something purchased add the purchaser as a member, and then trigger a sign up via the mail chimp widget without it being public?

Im awfully new at this, so apologies if Im missing something obvious.