What Do You Want To Do?
I like that the first point is defining use cases. It's too easy to start assembling vendors and doing a compare/contrast on features. But knowing why you want UC and how employees and customers want to use it makes great sense as the place to start.
Quick question: how "unified" can organizations expect a UC platform to be? My assumption is that no matter what vendor you choose, you're still going to end up with multiple products based on use cases, the need to reach out to people on different platforms, and pockets of users who've found a particular tool that really works for them.