capish, your #1 question/statement is correct. I won't touch your #2 one because I feel it's a method not proper for brugmansia cuttings. Why, if you wrap a cutting in a paper towel to send within days you will have nubs and when that happens it's best for the plant to be put directly into dirt for a better root system. The longer you keep them in water, the less likely your will have a good root system. You want to do what is best for the plant and not keep them in water all winter.
As for repotting, remember save your back first. To bump up to a larger pot wait until spring. I wouldn't prune roots until the plant out grows the pot you have selected to use.
General rule once every 5 years you should prune but when you do do not push the plant, you should forcus on allowing them to grow their roots and not flower. You might want to look into using smaller pots with holes and sinking them into a larger pot. If you want more information contact me direct. Remember some brugmansia do not like to have their roots disturbed so keep that in mind also.

Ok.... here's what I did this year. I have been over the past 2 years bringing the entire plant inside, usually it gets 6-7 feet tall. However do to space limitations, I simply cut off 2 branches, shoved them in dirt, and started me a new plant in a smaller pot. Doing this not only saved me space, but the plant is a lot greener as well. DO NOT break off the leaves, let them die on their own. Plants can hurt just like we do. I keep my brug inside by the window and allow it to grow all winter, but you can put it in a dark cool place (but not real cold) and keep it moist enough just to keep it from dehydrating.

Every year I cut around 60-80 major trunks and save them through the winter in five-gallon buckets (12-15 trunks per bucket)with a couple of inches of water in them. Come spring, I literally have to TEAR them apart, they've grown such heavy root systems. Most of these I carry to my local spring plant swap, the rest I plant in new spots in my yard for quicker blooms than I get on the new sprouts from the old rootballs. This summer, I never did get all of them into the ground, and right now I have several that are FLOWERING, still sitting in water in five-gallon buckets. And no, I haven't even fed them ONCE this summer!

Just don't believe it when someone tells you brugs won't grow a good root system in water!