I'm no expert But I'd say that rust is about normal for a 12 year old Jazz.On the plus side I dont think there are any recent applications of thick underseal etc intentionally hiding a potential multitude of sins. MOT testers are suspicious of such shenanigans. IMO the car should last many years yet, and longer still if any rust is treated.
But maybe too late to start regular expensive rust prevention treatments in the hope the car will last for ever and end up as a museum exhibit
I'm no expert either on bluetooth etc but AI says the following, (so it must be true

)
Bluetooth devices are not constantly transmitting at full power, but they do emit, at minimum, periodic, low-power signals to maintain connectivity or announce their availability, even when not actively transferring data.
Key details regarding Bluetooth transmission behavior:
Idle vs. Active: When not actively streaming audio or transferring data, devices enter a low-power, "sniff" or standby mode, checking in periodically rather than transmitting continuously.
Advertising/Discovery: If "discoverable," devices continuously broadcast signals to be found.
Active Connections: When paired and in use (e.g., headphones), they transmit in short, rapid bursts rather than a single, continuous stream.
I dont wish to alarm you further but you cant always avoid bluetooth transmissions entirely. They may come from a nearby car. Quite a few are transmitting in my home including, ironically,two fitness watches. range is only about 5 metres.
And also wi fi signals from neigbours homes etc.
I can understand concerns about mobile phones transmitting right next to your brain etc . But maybe any weak signals within the car might sometimes be an advantage if they allow handsfree phone use etc. (If the mk3 can do that).
I dont find the touch screen any problem when driving for quick changes where no great 'button' precision or though is required. Suject of course to paying attention to the road. The Mk4 still features some mechanical buttons which helps. Including volume ,seek and skip etc from the steering wheel. For more precise inputs such as entering addresses into the satnav the moving car can cause some misses due 'finger bounce ' . But this should only affect a passenger who can take their time. Its not something you should do anyway while driving