The upgrade checklist is def a good idea. Javelin has some good resources for this online, you should also be able to call up Cadimensions and get some guidance on this. If you are just doing an upgrade the main thing is making sure you get all the different servers (archive, sql, etc) updated right on the server and then keeping those clients all to the same version.
Hope things are going well up north!
Sorry, for the testing checklist I would just create a list of operations that covers the full scope of what you use the EPDM for in the office. If you use work flows push test files through it, check in and out, check user permissions on files, etc. With an upgrade whatever you do should effect the users in each group the same way, so you will know pretty quick if there are issues. IDK, just thinking from my experiences.