Types of implementation

You think of doing this, think of how to asking a good detailed question for a better reply to your one line question on a network implemention which is very detailed.

Rant over :D

Not much detail in your question but here is some generic advise.

First up you need to work out what is needed at each site, what can be kept local (the more the better), and what needs to be sent over the WAN.

When you are using a WAN you don't want to be sending huge amounts of traffic between sites. so one thing you should do is to keep as much as possible local to each site.

On the asumption that you are using Windows you should keep things such as a global catelog, DNS, DHCP server, and replicate AD. (not to mention resources for the users)

You should use a VPN between each site and only use it for necessary traffic (replicating AD and files that need to be shared over the link).

For any shares that need to be shared accross the WAN I would setup DFS between all sites.

Another generic bit of infomaton is that you should make sure you have selected the correct internet plan. You need to consider the connection type/speed for you network.

(You should really use a synchronous line or at least a connection with not just high download speed but also a high upload speed).

Make sure the plan has an appropiate bandwidth limit (business plans can be a killer if you go over your limit).