When the user has registered, we want to send a nice welcome email with an embedded video. how would I do this?

Hi,

You can edit the html template from here components/com_community/templates/default/email.html.php, but I think embedded code wont work for the email content.

Thank you

Is it possible to redirect the new user to a page upon activating their account with email? That would work as well.

Yes that is possible..this is the solution how to do that rselvakumar.blogspot.com/2012/08/joomla-...mail-activation.html