Today's K4 Server upgrade from version 6.6r4 to 6.10r2 went well. While I practiced everything on a test server first there was a hiccup that didn't happen with the test server. The lesson is to initially launch MySQL via the terminal and then read the error messages.
While vjoon is recommending InDesign and InCopy 8.1 we are still with 8.02. It seems that you need to subscribe to Creative Cloud to get ID/IC 8.1 but I am working on confirming this requirement since a test iMac allowed me to upgrade IC to 8.1 even though we had not installed it via Creative Cloud.
I do recommend using a service provider such as MEI the first time you do a K4 upgrade. It isn't brain science but there are many things that can get wrong, such as directory permissions and properly updating/customizing configuration files.
And I recommend cloning your server's boot drive before upgrading. The cloned drive can be cloned to your test system and will provide an emergency backup in case your upgrade fails. I also recommend making a copy of your data directory in case anything goes wrong.