Interestingly I made this same exact thing a few years ago for a company I worked at.

Raspberry pi connects to the printer, pi runs a daemon, Daemon connects to a central server and downloads stuff to print, server runs an API with a friendly endpoint.

Difference with mine is that I used CUPS on the pi and generated PDFs for it. I supplied a custom PPD to make the printouts extra crisp, but other than that the OS handled it for me. What I wrote was little more than a PDF generator and a basic spooler.

I can attest that this method is very reliable, if you're looking for confirmation that this architecture can be used in production.

I do question whether it's worth paying for this as a SaaS though. Speaking as someone who has built this, I'd probably build it again and it doesn't take long to get "good enough". The bulk of my time was spent on improving the printout quality from the built-in driver. Which was fun but unnecessary.