> -- customers who don't behave as well or kindly as before
Easy. Refuse service. You aren't legally obligated to offer your service to assholes. Any business has the right to do or not do business with whoever they want, provided they’re not refusing service for a reason that violates local, state, or federal law.
> -- customers who need 24 hour customer service
Also easy. You are under no obligation to meet peoples unrealistic demands or needs.
> -- maintenance that can't be done himself, and he has to employ people
He already is familiar with third party contracting.
> -- customers and vendors who sue you for breach of contract, or other simply nuisance lawsuits
Frivolous lawsuits are a risk in any business in America.
> -- upgrading the network to the next technology requirement, or when he's unable to get 2nd-hand parts so cheaply, etc.
What is this "next technology requirement"? My area cable company still runs most their network on 30 year old lines.
> -- or a natural disaster that unexpectedly forces replacement of (and charging for) equipment that wasn't anticipated in the original subscriber price
Cost of doing business, doesn't matter the size.
I think people don't understand just how profitable municipal broadband can be. It's why big players spend so much lobbying and bribing so they can keep their established position running and keep the gravy train running, but really the economics of it are fantastic once you've done the initial digging and running the lines, which sounds like he has here.
At $55 /mo for 400 households he's bringing in $22,000 a month plus whatever federal and local government subsidies and grants. The odds of a disaster, or one of the other scenarios you mentioned happening anytime soon is low, so he will have runway to build a decent sized war-chest to be able to easily afford handling any of these scenarios with third party contractors. The more houses he brings on line, the better it gets.