Edison's reference provides all (or at least most of) the details. In brief, you want to insure there's sufficient physical bandwidth to support your traffic needs, and QoS to insure that your traffic obtains it when it needs it.
Since you have MPLS shown for the WAN, you'll need to understand what the MPLS does with marked packets by default and by your request. If just two sites, you can manage the MPLS WAN without MPLS QoS support. If there is active MPLS QoS, you'll need to work within what it provides or can provide. (Edison's MPLS reference also mentions, something like MPLS can require remarking packets going into MPLS [and also perhaps exiting MPLS.])
