I think one of the easiest and most common deployments would be three connection servers in a replica group and a security server that is paired with one of the connection brokers. You then have two connection brokers for internal use and the security server for external use. You could go a step further to add the redundancy for the security server if you wanted. In this scenario the same virtual machines would be accessible both internal and external and then the View information would be replicated to all of the connection brokers.
Here is a link to the architeture guide for View 5, http://pubs.vmware.com/view-50/topic/com.vmware.ICbase/PDF/view-50-architecture-planning.pdf. I hope it will help you out.
