How to make LAN remotely accessible?

Hi all,

We've run out of floor space at our existing location (EL, LAN_EL). We're considering a new location (NL, LAN_NL), a few blocks away.

How can we make LAN_NL clients part of the LAN_EL so that LAN_NL clients see files of LAN_EL as usual, e.g. mapped drive letters.

Some facts about existing LAN_EL setup:

• Windows Server 2008 R2
• SonicWall firewall.
• The files are kept in project folders, each folder named by project number.
• Files are mostly DOC, XLS, JPG, PDF and AutoCAD files, some with sizes 2 MB or more.

Here is an idea. Still, I don't know whether it's a correct or standard approach:

1. At NL, setup LAN_NL server including RADIUS server, clients, and firewall.
2. I suspect trying to keep files always updated at both ends may be impractical. As such...
   
3. ... Setup company policy that only certain projects are accessed by LAN_NL
4. ... At certain...