I would like to be able to send Volunteer event registrations to one email address and Surgery registrations to another email address - is this possible or do they all they all go to whatever email addresses you input in that one field, regardless of category?
You can set Notification Emails for each event. Edit the event, look at Advanced Settings tab, there is a field called Notification Emails. You can enter emails you want here and these emails will receive notification (instead of the emails you entered in Configuration)