I have heard of several cloud screw-ups as well, leading to charges of several thousands.

On one side this can happen if you experiment something outside of the free machine(s), on the other side you have all the reporting and notification tools to avoid surprises.

Nonetheless, I still see your point, reason why I prefer to use an almost dry revolut prepaid for all the cloud accounts instead of my main credit card.

As you wish, indeed the only free offer without credit cards is the one of azure for students. In any case you are not anonymous.

Considering the small audience and purpose, I would not have any problem using the always free offerings of either Oracle or Google (the latter especially if located in the US).

I don’t know, wouldn’t the Hypervisor be able to track resources usage by itself without anything else?

If postmarket os works on that device maybe you can go full Linux (alpine), there will be no systemd which might be a problem and I am not even sure about docker compatibility. You can look it up though.