To be honest, SD cards are usually not meant for extending storage anyway. They should only ever be used for temporary storage like taking pictures and later transferring them to some other storage medium.
While of course Watchtower can be configured to not update and only notify there is also a nice, lightweight alternative out there that is built only for image update notifications: Diun.
I don’t think I would recommend a printer like this as an entry point.
Go with a Prusa (any of them are good, choose the right size for you). Or if you don’t care that much about open source, check out the bambulab P1P or the other ones from them. They are very good at multi color printing.
Basically your device (for example your phone) needs to know the ip adress of any service it wants to connect to. As you may know these services usually use addresses like Lemmy.org or google.com or whatever.
To know what IP adres is behind these addresses, you device needs to ask a dns server, in a local network (like your own WiFi) this is usually your router, but you can set it to any arbitrary device you want. This way you can see what addresses are being asked for by your device.
So if the app want to send data to some server, it usually needs to resolve the adress first. And you can see that.
It will go the way of Reddit…