The stages of a typical system install / upgrade would be as follows:-

Stage 1
Install and fully test wired / wireless network infrastructure.

Stage 2
Install and test new Small Business Server, including LAN & WAN connections.

Stage 3
Transfer all existing company data to the new Small Business Server, and test backup systems.

Stage 4
Install and test client desktop and notebook computers connection to Small Business Server.

Stage 5
Fully Document and maintain network infrastructure.