You can upgrade OS with SQL and use this moment to get to 12.6.2 or even 15

Yes, this one you can try

For 2k setup you should have cuic,livedata and ids on same box.Metadata exchange is not related at all

If you are on 12.5, you can always open TAC SR for the help.It is very difficult to help you with such request, as there might be multiple causes of such behavior:1.Wrong credentials used2.Wrong user configuration on AD3.Certificates are not exchange...

You can get ES for 15.0 via TAC SR