1)Hang onto your bike-it is PLENTY sturdy.
2)With proper preventive maintenance it will last "FOREVER"
3)With ZERO preventive maintenance- it will last almost forever-no kidding folks who ride bikes because they have to-never bother with the compulsive chain lubing cable lubing cable adjusting brake pad adjusting folks here do
4)So forget getting a single speed because of reliability or less maintenance concerns.
5)No you don't even have to lube the chain.Chain lubes ALWAYS attract grit-which ALWAYS grinds away at the "sprockets"
But the sprockets STILL last 10,000 miles-lube no lube
So if you want a single speed because it is COOL-fine-but manitenance or reliability-??
If a shifter or cable breaks you can still just run it as a single speed-make sure you have tiny multitool with screwdriver-so you can Push the derailleur onto the gear you want.

Your bike-fine bike-get a multitool-carry a spare tube or two patches midget pump- tire tools( tiny pry bars) in a bag of some sort-fanny packs are kinda "funny" looking but I carry one because it is so functional-(get an "good"actual pump-not BS CO2 driven-POS-SOMETIMES- you have multiple flats-SW folks have HORRIBLE burrs-god must hate them)
If you like to oil things spray the chain every year whether it needs it or not.
Hose it -entire bike-off (simple green etc)when it is filthy-pull seat post-make sure it drains(upside down)-about it for maintenance

PS Bikes are almost owner proof-always have been except maybe some French components-hard to break them "shifting wrong"-even with friction shifters derailleurs-it took a REALLY heavy handed owner to actually break a component(assuming it wasn't some quirky French bike component) If a French component didn't like your accent -it might break!