Reporting back, as promised.
It’s running. I built it on Cloudflare (Workers + D1 + R2), and it now handles the licensing for my Shelf extension — checkout, licence, activation, seats.
The surprise: the server was never the hard part. There is no machine to patch and no uptime to babysit, and at my volume it costs close to nothing. If server management is what’s putting you off, that fear is out of date.
What actually cost me days was the seam between the payment provider and my own database. Those failures never threw an error — every log looked healthy while nothing reached the customer. So: test every link in that chain, including the boring ones, and check that deliberately breaking a step actually turns something red.