Intranet drupal sites and one Central Internet Server

Hi

Is it possible to build a system for an institute which is structured as follows :

• The system is for an institute that has many branches spread geographically.
• There will be one central installation of drupal available on the internet.
• Each branch will have a copy of the central site on the branch network (local intranet).
• Internet may not be available on the branch network.
• The central server is to be synchronized with the local intranets.
• Users on the local site should be able to login to the Central site and should be able to have a similar experience.

If yes, then can someone guide me on how to get started?

My initial thoughts:
1. use a multi site module
2. create the central server and all the branches
3. copy the site to the local network in the branch with only the data relevant to that branch. The local may however have all the other central configurations to reduce maintenance but not the content.
4. periodically, the local will be synchronized with the central site. Now, here i'm even open to a method where the database from the local is backedup and sent/transported to the central site.

So the core objective is, the local site should run within a local network and there should be a mechanism to sync with the central site.

Thanks
aps