Thanks - working on it as we speak :)

You need to install New DC on Windows 2016 and set it as secondary DC in your forest.
Then you need to transfer FSMO role to new server, then rise level to Maximum available option.

Sorry, but this to me is nonsense.  There is no such thing as a secondary DC.  Everything is a DC in active directory.  You don't do anything special to "set" a DC beyond the default DCPROMO.  You CAN optionally transfer one or more roles, but you're not setting anything.  And you don't need to raise domain or forest functional levels - you SHOULDN'T until and unless you no longer expect to have DCs of a particular vintage.  For example, if you expect to NEVER AGAIN have 2003 DCs (and frankly, you should), then you set the Domain and Forest Functional levels to 2008 once all 2003 DCs have been removed.  If you are SURE you won't have any 2008 DCs then you can raise it a step higher, and so on.  But there is no NEED to do these things and frankly, you should not do them unless you KNOW you can!