Nick,

1.) When clients purchase hosting, domains, etc through CE, they will automatically be synched with Joomla, correct?

Yes, as long as you edited the proper ClientExec signup files according to the instructions.

2.) Joomla has various Groups: Author, Editor, Publisher, Registered, and so forth. What is the default group that new clients are set to? Is there a way to specify which group new clients are set to in Joomla! via the CEBridge?

The default group clients are set to is "Registered". At this time there is no way to change it without editing the php code. I set it up this way because I assumed no one would want clients to edit there Joomla site. You can however, use the ClientExec Bridge User Manager to change the group for clients that may need it.