A. Yes, members can have capture pages add contacts into a specific contact group. Also, they can transfer contacts betwen contact groups.
A. Go to advanced features - under misc tab you will find something called "
Manually Adding Contacts" ,this is where you can control how many contacts your members are allowed to add.
A. No, they are 2 separate things.
Setting up a contact group allows you to group your contacts by specific criteria. IE: active contacts, inactive contacts, etc. You can assign each contact group specific autoresponders, and even specific capture pages.
Trackings are created to track where contacts came from IE: facebook, or a specific capture page.