OK, I'm Starting to Think Bike Specs Again

I thought I had the "power cuts out" thing on the Nakto e-bike whipped. It performed perfectly on a three-mile ride yesterday. Then, today, it suddenly lost power near the end of another one. Just for an instant -- as soon as I let go of the throttle for a few seconds then twisted it again, I was back in business -- but since I apparently didn't fix whatever the problem was in yesterday's "check all connections, tighten everything," I'm probably looking at something I 1) can't fix myself and 2) wouldn't like the price of having fixed at a bike shop.

So, I think I'm in the market for a new bike. Or, rather, a used bike. I saw some stuff on Craigslist -- all from the same guy, near me, apparently he fixes them up and sells them, in the $150-$200 range -- that fits into my general desired specification:

• Single speed. That one is probably the closest to non-negotiable. I live in a relatively flat area. I don't need 21 gears for zipping up and down hills. And I don't want the additional complexity of cassettes, derailleurs, and associated cables and levers. The simpler the bike, the less to go wrong and the easier to work with when something does go wrong.
• Caliper brakes. Same reasoning. I don't dislike e.g. hydraulic disc brakes, but I'm comfortable adjusting and replacing pads on good old-fashioned caliper brakes. Less to go wrong. Easier to fix. I don't like coaster brakes (the ones that engage when you pedal backward) because they offer less control and are more of a pain to replace when they wear out than caliper brake pads.
• 700c. The current e-bike is 26". A 700c felt awfully damn tall the first time I rode one, but once I got used to it I found I preferred it.
• 57cm frame. I might be OK with a 54cm. I'm right on the recommended height borderline between those two. But I've had two 57cm frame bikes and liked them both.
• Not unduly narrow tires. The only thing I disliked about my old Critical Harper was that the narrow 25mm rims fit tubes with a Presta valve, rather than the normal Schrader (the kind of valve on your car tires, the kind of valve every gas station air hose fits). I'm pretty sure I need to get up to at least 30mm if I want to rock Schraders. Otherwise I'll either have to rely on a pump I carry with me, or buy some valve adapters (my past experience with those is that they're hit and miss). I might be talked into a bike with narrow Presta-valve rims/tubes, but if I can avoid it I want to.
• Electric? If the guy has something fitting the above specs and the price is right, maybe. If not, I might consider buying a conversion kit. BUT ...

My weight loss has plateaued. Instead of ballooning back and forth between 220 and 250 pounds, I balloon back and forth between 210 and 220. I think getting back on a bike might let me get down below 200. And I think if I get below 200, I may not blow my knees out every few months when I get so into the cycling that I'm doing 100-150 miles per week.

I've already talked with the spouse about reining me in if I seem to be cycling too much. But I think it's time to start cycling more with my legs and less with a throttle.

As for the above specs, everything else is easy. If the bike I want doesn't have a rack, I can pull one off another old frame. If the bike I want doesn't have integrated lights, I already have a cool USB-rechargeable rear light and a holder for a small flashlight for up front. I think I may buy one of those little bags that fits on the top rack to hold my phone instead of using my current handlebar holder. I may replace my pannier bags, as they've been used hard and are probably on the verge of throwing a zipper or getting a rip. I've got a bell or two I can mount for signaling. I've got locks.

If I can just get a single-speed 700c/57cm with caliper brakes at a reasonable price, I'm golden. And I may do that as early as this weekend.