In Sharepoint, how do you setup a column for ‘person or group’ with a default value

You cannot set a default value for a column in Sharepoint based on the content type. What you could do though is modify the editform and newform aspx pages of the lists that use the content types / columns and then use JQuery to set the value based on the selected content type.

If you want a no-code solution, create a Workflow with Sharepoint Desinger. Follow this tutorial http://office.microsoft.com/en-us/sharepointdesigner/HA102390421033.aspx, just when use a field from current list item in the "to" field instead of constnt string.

If you can deploy code to your server, you can create an eventhandler that catches ItemAdded event and send your e-mail from code.