k_graham
SME8 is essentially the same as SME7.x, although of course there are additional features and improvements.
Please read the release notes at the beginning of the SME8 Forum to see what changes there are in SME8.x
Refer also to bugzilla.
As I understand it the Manual wiki pages are locked and only editable by contribs.org admins.
You could request access and start creating a new SME8 manual.
Look at your Forum profile for details.