I recommend you
read these pages. There's tons of info there that will answer these questions and
more.
However, since you asked: ribs will have to be scrunched in,
sliced in half or curled on an 18". Likewise, a
packer brisket will have to be shoehorned between the cooking grate handles or lumped over a brick or rib rack or something. Once it shrinks after the first few hours it's smooth sailin. A 22" does not require these special tricks.
All the WSM(s) are VERY
portable. Most folks put them in the back of a truck or on a hitch hauler to go to comps, camping, etc. Some have dedicated comp trailers.
I use lump and briquettes of all brands. Many swear by and only use
Kingsford. Here's an article about
charcoal.
The stoker will work great with the WSM. Many comp teams as well as casual users use them with great success. I've read that it holds temp +/-1 degree once it locks in. However, I have had great success running a naturally aspirated WSM. ...but I am a weekend warrior and don't need that level of accuracy.
The only
accessories I think are must haves are a
chimney starter, a lighter, a pair of tongs, and a cold beer. Other than that there are a lot of toy, gizmos and gadgets that are fun to have.
Big Green eggs are great but I think you'll be very happy with the versatility, portability, and initial cost of the WSM. One of the best features over the egg in my book is
the access door. I can add charcoal or tend the fire but my brother - an egghead - can't without disassembling his cooker.
I hope this helps get you going. And most importantly - Have fun!