I can't answer most of those, but:
We used to camp in winter temperatures - in fact I've been in it on nights as low as 17 degrees F. You'd want to use the tank instead of city connection, but it's fine. The only two issues I've had doing it were:
--One time the one dump valve froze a bit. This could have been avoided by putting some RV antifreeze in the tanks.
--Another time a little water froze in the city connection. It was only a problem when I went to winterize after the trip, and it was just a matter of running some antifreeze into the line.
To hook up a second propane tank, you'd need someone qualified to add in a connection for you, assuming it's even possible - I'm not sure. This is something I don't like about motorhomes - that is, how the tanks are permanently mounted. I actually *enjoy* getting the tanks on our trailer filled now. But how long are you going to be staying? You should be able to handle two or three days on propane without a problem even with the furnace and water heater running.
You wouldn't be the first to do this with the B190 - there was someone in Colorado that did it, too. I seem to remember him saying that the B190 was actually pretty good in the snow, because of all of the weight. I have not tried it myself.
I don't know what the load limit is, but I've been up on the roof (~185 lbs at the time) several times without a problem, though I did try to spread out, too. Additionally, we had what we lovingly call "Snowmageddon" here in DC a couple years ago that left 18" or so of snow on the roof of our B190...no problem.