1. didn't found any good maps where you can see on which parts of which rivers you can do that on the germany. Some guy from youtube recommended the best way would be to order some analogue printed out map from some book publisher like a boomer.
2. they are not that cheap and even if they were I fear that I will do it once, feel like it is not worth the effort and then put it into my attic for the rest of my life. And then I will have to carry it with me whenever I move flats.
3. I never camped in late autumn outside and especially not in the rain. I will try it in the next couple of weeks just to see if my equipment is good enough just to try it out but that will probably be it for the year. Also these packrafts basically don't isolate you from the water beneath you. So if the river is really cold it will suck out all the heat from you. So I would prefer to do it in summer.