Tony,
What kind of sausage do you like best for bangers & mash?
I thought it was pretty delicious with cumberland-style snorkers. Do you have a favorite?
If you want a 22" WSM I wouldn't beat yourself up over $50 on the price one way or the other. You won't regret spending that extra money once you start using it, I can almost guarantee that.
I would imagine that allowing drippings to hit the heat source is for flavor. When the fat vaporizes it adheres to the surface of meat just as smoke from wood does.
Michael,
If you want a smaller fire from the large chimney, just use fewer briquettes or coals.
I think the Weber expandable hanging rack is a must-have accessory especially for the 22" WSM. But you certainly don't need it to get started.
Anything you can jam a spit through or fit into a basket you can cook on the rotisserie with fantastic results. I wouldn't try custard pie.
There's lots of great rotisserie attachments available you can use for more capacity, to tumble food, & etc.