I think you should also checkout TRMNL. Being engineers ourself security/privacy is of atmost concern, and we follow a similar architecture mentioned above. You could create a private plugin and send in data in the form of REST APIs[1]. You could also use your own webserver by hacking the firmware[2]

[1]-https://help.usetrmnl.com/en/articles/9510536-private-plugin...

[2]-https://github.com/usetrmnl/firmware/blob/main/include/confi...