| Short novel starts here.......
There are no pressure sensors in your wheels - those are only used in North America, not Europe - the tyre pressure warning is triggered by the ABS sensors saying one wheel is turning faster than the others and so the computer assumes it's flat. So your S-winders are ready for use, as they are. A good choice too, being a lightweight wheel, though maybe a bit of a bugger to keep halfway clean in winter?
Your car is not 'set up for runflats' and it will work just fine on non-runflats. If the car had come from the factory on non-runflats, it would get an emergency pack in the boot consisting of a tyre compressor, a jack and a cannister of tyre sealant. I presume you get a jack, even with runflats. So you can either buy a tyre compressor and sealant, or trust to luck and the AA/RAC.
I've gone through a couple of sets of winter tyres and my opinion differs from most peoples' - if you fit your winter tyres for the winter, and not just when it snows, then you will be driving on wet or dry roads 95% of the time and I prefer to pick a winter tyre that works well in these conditions. As far as I can tell, any decent winter tyre will be absolutely brilliant in snow and slush, by comparison with summer tyres, so picking which one works best in snow isn't important.
I can't see the logic in waiting for snow to fit winters - to me, at least half the benefit is being able to drive safely/quickly on roads that may be icy and might not have been gritted. So that means having the winters on the car for four months or more, hence you want them to work well when there isn't any snow. Last winter I didn't get much use from my winters in snow/slush an could have got by on summer tyres - but I had two cases of finding a minor road covered in ice and the winters saved a crash both times. One of the roads had a 5-10 metre drop off the edge, so the winters probably saved me rolling the car over.
I have a set of part-used 16" Nokian WR G2 winter tyres which I'll be selling cheaply once winter starts, but they are already on a set of 5-star wheels so may not suit you. These Nokians are the nicest winter tyre I've yet used, but then I've only tried them and some Pirellis. The Nokians are little short of unbelievable in slush - I can drive on and off the mounds of slush between the wheel tracks and I can't tell when I'm driving on slush and when I'm driving on bare road, whereas summers would be twitching violently in these conditions.
I still want better wet/dry road performance from my winters so this year I'm going to treat myself to a set of 17" winters, which is why the Nokians will be for sale. Like you, I've even bought some wheels for winter tyres before my new car arrives!  | 
