I'll say "ditto" for post #3. I manage 7 sites with about 1800 TDM devices, 4 call centers but only one of them has 50 people, 330 cellular devices, UPS devices, yadda yadda, and am 98% self maintaining. I wear a leash 24/7/365, and it is almost impossible to take a vacation and enjoy it because things only blow up while I'm on vacation (or 3:20 PM Friday afternoon). In a mess this size there NEEDS to be backup. Not just for vacations, but also for illnesses, multiple simultaneous moves, covering time for administrative crap like budgeting, ordering parts, paperwork, designing upgrades and the like. I had some help for a while but the guy who was helping me works for a different department that got outsourced, and the company they were outsourced to doesn't want him doing any work outside of their contracted scope of work.
So I would say 2 guys for those reasons, even though one guy is doing it with a backlog of around 50 work orders at any given time. You don't want to run with no backlog because then you have people sitting around without enough to do and they will either heap on more stuff for you to do that will never go away, or cut your hours.