Help me Spec a Server

I need to spec a server and want to make sure I don't under or over power it.  Going to run Hyper-V with 3 VMs.

- Windows Server 2012 with Active Directory

- Windows SharePoint 2013 Standard

- Windows Exchange 2013 (combined Client Access Mailbox Servers)

I also plan on using Hyper-V to provide failover VMs. 

Recommendations on memory, processor, disk space, and Dell model are appreciated.

Thanks.