As I said above, digital wireless is interference-free. Analog wireless not so much.
I'm not sure what you're referring to. Once I line-up the the magnets and the sensors, that's it, unless you move one or the other. I found cadence magnets stay put better with a wrap or two of electrical tape. I use the waterproof stuff.
Only with wired ones on the front wheel.
I'm back to looking for a wireless!