I don't think you could even have anything approaching 1970s level of tech and be self-sustainable in a small city. Would you know how to make a discrete transistor? How big a community would you need to spin up even a basic electronics factory?

I think 50,000 people means you're not even at the industrial revolution level of tech. You're certainly not going to be able to manufacture any electronics. That completely limits the power generation options. Also, you'd have to use pretty basic materials, because 50,000 people isn't enough to have advanced materials processing facilities. You'd also have a severely restricted diet, growing only whatever the local climate permits. It would probably have to be vegetarian, unless you had enough space for hunting (with bows and spears).

One of the more misunderstood things about Amish people is that they cant have anything electronic. They arent against electronics. Like you said they practice self reliance above anything else, so they refuse to use anything that is powered by oil and gas because they cant make oil and gas products themselves.

One thing that has become really popular with the Amish is EBikes and solar power. Theyre fine with buying those things even though they dont produce them. And theyre fine with anything that runs on solar power because they have plenty of access to the sun.

Im not sure exactly how the loophole works that allows them to buy solar panels, since they aren’t producing them on their own. But the bigger thing to them is that the source of energy itself is widely available to them, which isnt true of oil or gas. Maybe it is that they could theoretically harvest solar power in other ways, so they are fine with buying a more efficient way to do it than what they can produce within their community. Something like that