No, Internet is not essential, but helpful of course. The biggest issue will be getting updates. You can do a telephone activation with Microsoft.
Personally, I am holding off on Windows 8 -- I see too many people with driver and other issues that will take some time to go away. I run one copy as a virtual machine in VMWare, which has not had issues, but I'm also just not ready for the interface change. Being old school, my Windows 7 still looks as close to Win 95 as it can.