It's impressive, but, at the same time, I'd imagine it's way too stressful to run by yourself in a small town like that. Without really that much payout, money-wise.
It may sound like you might be spending something around 20 hours per week on this, if not more. If you bill your own time to your new ISP at market rate, when will you recoup the investment? Is that still 4 years?
To put some math into perspective, (20 hours/week * 4 weeks/month * 100 USD/hour) / 50 USD/month/customer = 160 customers -- that's how many customers you need to cover just your time alone, without considering any other expenses. The math should definitely work out given an adequate intake, but I think it's also easy to get lost in the community and tech part of it, forgetting the business case. Especially if you live in the middle of nowhere, without that many neighbours to sign up.
As such your calculation does not hold and 160 customers will not be needed to recoup costs, cash or non-cash. There need only be enough customers to cover running expenses, administration costs and once off investment costs over time.
The thing I most wonder about if you start to be a service provider and need to provide ongoing connectivity - you need a backup plan for when you're out of town.