Fibre draws almost f-all power, should be on the box/fibre converter. Laser printer on the other hand is beach. has rather spikey power usage.
Also, don't by normal UPS, the battery's are not made to cycle more than few times, its for backup .. not often use. Also, they take about 24 hrs to recharge, so never charged on stage 2 shedding. lots of people is learning this the hard way at moment.
UPS is just a inverter /charger and battery .
Very basic setup:
Buy a Kodak/Axpert or what eve 12 or 24v inverter .. get 2 x >100 gellcell deap cycle type battery (no fumes) and connect a multiplug into the output and plug the input into a wall socket with 3 point plug.
ITs fully legal as its not permanent and have all the disconnects needed
Will cost about R10k
Later when you know/learned more .. get things done proper 😉
EDIT: disclaimer .. there to many question, i'm to old to keep track of all so i'm answering in general