1. They're easy, if you can simmer them a bit. Adding boiling water and using a cozy doesn't quite do the trick.
2. Powdered instant milk works fine with them.
3. Note: I use a 2 qt. pot because that's my setup, so I can't answer from direct experience. I suspect a very deep and narrow pot would make stirring difficult, especially if the contents of the pot come nearly to the top. As far as the actual cooking goes, I don't think it would make much difference.
4. I use an Open Country 2 qt. uncoated aluminum pot with a wire bail handle. Stirring is the best antidote for scorching. See answer 3 for further thoughts on stirring.
Other thoughts. The Knorr Sides are cheap enough you could try a few at home and decide if they adapt well to your normal cooking setup and they taste good enough to enjoy. They work fine for me, but YMMV.