Auditing Domain Administrators – Best practice / Advice needed please

Please do advise if I am posting in the wrong place, I have not found this the easiest site to navigate (or maybe it is me…).

I have been tasked with auditing and fixing our privileged accounts after a Microsoft CSAT scan. I have inherited an absolutely shocking number of accounts that are ‘affective domain administrators’ – 293!

It seems the previous attitude has been security anethema – giive service accounts Domain Admin status to ensure they are not part of the problem… sigh

I have investigated numerous powershell options and come to the conclusion that I need to:

1. Find out which SERVERS each account is authenticating against (Inluding DCs obviously).
2. Find out the least required access for each server.
3. Amend access accordingly and test.

Would anyone be able to advise on the best way to proceed please?

Thank you in advance.