This is a very small development system and there is not a dedicated IT resource. It is a single hosting server running 2012 R2 with all its hosted VM servers also running 2012 R2. There are a few Windows VM workstations as well.
There is currently a natural break in activity that makes this a good time to move from TFS2013 to TFS2017. This will also involve upgrading other core applications such as SQL server and SharePoint. Since the whole development system will be going through a major transition, upgrading the server OS's at the same time seems the right thing to do. So, several questions:
1) Does the decision to upgrade the server OS's from 2012 R2 to 2016 make sense? Are there any significant downsides to going away from 2012 R2 at this time? I understand there are always many potential issues, but I'm hoping for some general higher level input.
2) Are there any significant issues restarting the existing VM .vhdx files in a new host 2016 Hyper-V? My thinking is that once the hosting server is upgraded, I could keep the old TFS in the background in case something delays getting the TFS2017 smoothly online, as well as maintaining access to that machine's SharePoint installation.
3) Are there any significant issues restarting the existing VM 2012 R2 domain controllers (primary and secondary) and then transferring their AD DS to new 2016 DC's?
Added after initial post:
4) The hosting server has a moderate amount of necessary configuration and apps for the sole purpose of serving as the host. This includes backup, dynamic DNS management, UPS interfacing, etc. Would leaving the host on 2012 R2 while only upgrading the hosted servers to 2016 be a reasonable alternative?