Question : Exchange 2007 multi-site design

I am looking for documentation or recommendation for this scenario:

Organization has 5000 users at a main physical location and about 4000 users spread out across the country in approximately 600 offices with users ranging from 2-50 per office. Small offices have current messaging from Exchange 2000-2003, POP, and Lotus Notes.

Questions:
1. Would any server be deployed for the smaller offices? If so which roles and where?
2. What would be some recommended migration methods for the small offices with users on POP or Lotus Notes?

Answer : Exchange 2007 multi-site design

For very small offices, I would possibly be looking at something centrally located in a data center somewhere. That gets round the bandwidth issue. Then have a VPN or similar to the larger offices.

Simon.