Once you have everything spec'd out, then you can design the internal/external data pathways and system connections needed to deliver on them, and decide on an app-by-app basis which would work better on the new platform or the old.
The most important part of the rest of the implementation isn't actually doing the work. It's making sure the contracts you sign with SAAS and cloud providers require them to deliver what you actually want them to deliver, not just generic promises about the dynamic availability of resources.
Detailed guidelines useful enough for you to plop them into your own plans are difficult to come by, but you can get to the same place by asking the right questions.
Here's a list of some of the questions that will cause trouble if you don't get good answers, risks you may not be sufficiently aware of, and ways to mitigate both.
Ad hoc course on cloud implementation: