Hi Troy,
I'll tackle your questions in reverse order as this is how they should be addressed from a design point of view.
Simply put, no, there is no need to have any physical servers running alongside Exchange 2010 VMs. The only reason that might have been a requirement in the past would be support. Since August 2008 Exchange has been supported on vSphere versions as far back as ESX 3.5 Update 2. Exchange 2010 SP1 included support for the Unified Communications role to be virtualized.
How many VMs you would require to support 1300 users can vary greatly depending on your design and hardware. Honestly, you could support all 1300 on a single, properly sized VM. HA requirements will typically dictate the need for redundancy at the various layers of Exchange. If you are planning on using Edge servers you will need at least two of those, you will need at least two hub transport and client access servers. Those last two can be combined, which is very common, and can help reduce server count. Finally you would need a mailbox server. Whether you choose to go the stand-alone route, multiple stand-alones, or use database availability groups will determine how many servers you end up with. The three internal roles can also be combined into a "multi-role" server which has the advantage of reducing your server count while providing redundancy. The disadvantage of the multi-roled server is that it can be difficult to troubleshoot and perform maintenance on. At a minimum you are realistically looking at 4-6 servers including Edge server roles, 2-4 servers if no Edge services are to be deployed.
Migrating from Groupwise to Exchange is a well documented process, however there are no native tools for the task. You have the option to start fresh; stand up the Exchange environment, create mailboxes, get mail flowing and archive existing mail, or go down the migration path. I've included a couple of links from MSExchange.org that are a good starting point. I've also included some links to VMware documentation that can give you most of the info you need to begin your journey to successfully virtualizing Exchange on vSphere.
Any questions, don't hesitate to ask!
-alex
http://www.msexchange.org/software/migration/
http://www.vmware.com/solutions/business-critical-apps/exchange/resources.html