Is there a way I can set a default k2 user when someone signs up from the front end of the website?  Currently when they sign up they are put the default Joomla user group but not assigned a K2 group.  How do I set up for them to be assigned a K2 group at sign up?

You can select the K2 user group for the users that register in your site by choosing the option: Select a K2 User Group in the General K2 parameters.