It is nice to hear from you again.
The security model of Sitefinity 3.0 is not different from that of Sitefinity 2.7, that is, you are not allowed to set permissions directly to the users. The permissions are set by Roles and all users assigned to a given Role inherit the permissions defined for that role.
What you have to do is create 2 roles:
one for the registered users
one for the non-registered users.
Set the appropriate page permissions for the two Roles: allow access to the relevant site parts for the Role containing the registered users and forbid access for the Role containing the non-registered users.
Also, you need to restrict the anonymous access to the CMS administration. To do this in Sitefinity3/Admin/Web.config, you should set:
<deny roles="Anonymous" users="?" />
At this stage there is no e-commerce module developed for Sitefinity 3.0, though we have planned to implement this functionality in one of the upcoming releases.
I hope this information will help you. If you come up with more questions, do not hesitate to contact us.