Please see the demo video (http://www.jevents.net/jevents-club/demo-videos
) that may answer some of your questions.
1. there is no way to import a list of invitees BUT you can save a list of invitees that you have used to use again in the future. This list is private to the event creator - i.e. only the creator of the list can reuse the list. The list is in 2 database tables #_jev_invitelist and #_jev_invitelist_member
The data format is very simple so you could create a series of lists using a csv import from phpmyadmin fairly easily.
2. Invitees can be joomla users or email based invitees.
3. You can restrict registration to only those invited to attend and have an additional option to hide the event from non-invitees completely.
Note that email based invitees will only be able to access the registration by clicking the link in the invitation email they are sent.