No drivetrain is 100% maintenance free. Anyone who tells you that is lying. Singlespeeds are a bit easier and cheaper to maintain, since there's very little fiddling involved. But you're still going to want to take a poke at it about once a month, to make sure the chain is secure and isn't wearing out. A belt drive will not have chain lube, but is otherwise about the same. I don't know about belt drives, but the usual plan on singlespeeds is you replace the chain, chainring and cog all at once. I'd guess you would start thinking about the swap about every 10k miles or so.

It sounds like you *might* be a good bit like my partner in terms of riding style. He's a smallish Clyde (about 220-230lbs), with short stumpy tree trunk legs. Mostly on a bike he gets by due to brute force... which would be fine except he has to keep up with me. I'm a lot smaller, and I am not very strong at all, but I can spin. And spin. And spin.

He did go singlespeed, but he's riding a much lower gear than he's used to, and going a lot faster. He knew going in that singlespeed would force him to learn to ride a bit more like me, and that was a big draw. So far, seems to be working. Before, 10 and 20 mile rides were very hard on him. Now, the problem is never that he's running out of gas in the legs, so it's a big improvement.