WAN Planning, Design and Implementation

Our company is a middle size (and growing) financial institution with six (6) branches in the geographical region of the country. I am the IT staff in charge of the WAN implementation. I have never implemented WAN before but I have implemented LANs. Could any one help me with a good solution, that is, what do I need to put in place, to make provision of, the type of link to use, the bandwidth, and so on…Thanks a lot for all your contributions.