Steve, this is a good list. I will keep it for future reference!

When you mention "side-by-side" migration I assume you are using the same host name for the new server and SQL Server instance?

For me, this has been the biggest challenge in these type of migrations before.
In virtual environments you can setup private networks to isolate the new server from the production network.
But sometime there are many third-party applications that must be tested before the new server can go on-line.
Some external systems also use hosts files where the IP address/host name is hard-coded.

I am looking forward to see the responses on this forum.