The first request - tracking changes through comments - hasn't got a specific method. You can certainly make comments when you publish - down near the "Publish" button is a comment box to enter change details, which get published on the Page History.
If we do need to store announcements / important edits to a page for users to view - we often use an Info Box at the top (one of the macros).
For the second however, there are applications for that - such as Comala Workflows.
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