My domain at work is very large 8 Windows 2008 R2 DC and 1 RODC in the DMZ. We are looking to upgrade our domain to Windows 2012 R2. Would like to go to Windows 2016 but way to new since it just went GA this week. I need to keep the same DC names and was planning on take one DC demoting it: doing a fresh install of Windows 2012 R2 then promoting it.
1) Should I do the DC hold all of our FSMO roles first or last for the upgrade?
2) Would it be better to add a small temp WInodws 2012 R2 DC just to introduce a Widows 2012 R2 DC to the environment first or not need and just take an existing DC and demoting it