To give you my take on these questions:
Except when his link blows up I suspect he’ll press the equivalent of the WiFi kill switch on his gear!
By RAW, if he wants to do anything through the matrix, he needs to have a persona – only then can you use matrix actions like control device.
You can of course push physical buttons, but as soon as your PAN is down, you need to address all your gear individually, since you are no longer in AR.

The next target would include the trode net, so his DNI is gone too (which would make it nearly impossible to switch off everything (contact lenses for example are pretty hard to control without AR)

Although if his PAN is gone is the gear WiFi at all???
As long as his gear doesn’t receive the order to shut wifi off, it will stay on.

I’m sure it should be possible to rig a ‘big red button’ that when pressed (and only physically pressed) sends a code to alert devices to shut down. Sure the devices could be spoofed but they can be anyway…
Theoretically, but that isn’t exactly supported by the rules. Such a device would have to be wifi enabled and is therefore very vulnerable against hackers – which kind of defeats the purpose – especially since Isaint has his Jammer running, so the shut off button would need to have quite a lot of noise reduction as well.

The most viable method to create such a device would be to have all your gear directly connected with wires to this shut off device, but that would make it very hard to handle your gear. (For Vindariel I’ve build such an armor with an integrated deck, wired AR gloves with a modded touch receiver, so I can pick up my guns and create a direct connection without having to connect any wires)