Hi Adam, this is a very advanced topic and I would definitely recommend the Advanced Q&A webinars ( http://www.clarizen.com/live-demo.html) or some consulting time with your CSM to properly set this up.
There are no Work Item Interact rules by default, so you have to create a new rule from scratch. The Interact tutorial videos are a good starting point. For the toggle options, you can either hardcode them into the rule (ex: if Urgent is in the subject set a certain toggle to be on), or you can have people enter the field into the body email along with TRUE/FALSE (ex: Urgent: TRUE).