It can work as long as the phone has an option to limit the battery charge to 80% or less. Keeping the battery fully charged for an extended amount of time will damage it and may even cause it to puff up.

There are cheap USB cable testers that will tell you what pins are connected and what speed the e marker chip reports. Actually measuring the bandwidth of the cable requires some expensive test equipment though.

No, they are supposed to start delivering then later this year.

If you want to go the DIY option for a 3D printer, there is Voron. It’s open source hardware and it runs the Klipper firmware which is open source.

The Slate EV doesn’t have any telemetry.

There are still phones with FM radios. They’ve gotten harder to find since they need wired headphones to use as the antenna. I’ve never seen one with an AM radio though. The antenna in a pocket AM radio is thicker than a modern phone.