Get the necessary managerial permissions to lock down end-user rights and then then pause automatic updates on all computers.
Start with your most problematic end users - you probably already know who those people are.
The people most likely to scream will be managers and those who game, shop, watch sports, etc. during work hours.
Pausing updates is an administrative nightmare but necessary if some update catastrophe is to be avoided.
Eventually Microsoft will override the pauses and force the updates.
Set up a couple of computers that are representative of end user configurations. Clone or image them for fast recovery and allow immediate updates to those systems. May help catch some incoming problem before all systems are hit when an update is forced.
Immediate needs for "brushing up": You will need to set up remote access so you can manage individual computers from one location. End-users may be in the physical office, at home, or perhaps "on travel" (TBD).
Get ahead, prepare for that scenario and what you need to know and do to provide IT support accordingly.
Having project management experience is a plus. Treat the IT requirements as a project that you are managing. Even though you will be doing all the hands on work as well.
Create your own project plan and be ready to present the plan to management. Avoid tech-speak, use a few simple diagrams and charts. Establish goals and plans of action. Present the proverbial "The Good, The Bad, and The Ugly". Being realistic is not being negative.
[Note: You probably know a lot of that but IT presentations can quickly glaze over eyes...
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Try to get some help. Odds are there are two or three other folks in your office/company with IT inclinations and experience. You probably know those people as well. One way or another....
Get management approval to recruit them, the truly helpful people, as well. You will need help
and backup.
Management does not need to give you carte blanche (and you are not asking for that) but they do need to allow you to do the job.
Hopefully keeping management up-to-date on situations, problems, risks, expenses (labor, materials, resources) will keep them at some operational arms length.
To be blunt, if management is not supportive, then your days and nights will become very difficult.