Migrating to Windows 2000

My workplace has 27 remote branches all running a WinNT network (including the head office making a total of about 30 domains). We are planning to upgrade the whole network to Win2K but wants to start with the head office.

What is the best way to go about this to minimize the pain? Will the outside branch PDCs work well with an AD Win2K head office domain. What about Exchange 2000??