Larry, I will give you the answers to MY process. I am sure others will differ.
1. I do not trim pork butts. Most of the fat will render out and I even leave the fat cap on.
2. Do NOT pull out the bone. I run my temp probe on the other side of the butt to make sure it does not touch the bone.
3. I would not smoke two butts unless I needed it at the same time. I would throw one in the freezer and brine the other so I cannot really answer about a lower rack. However, If I were to cook both at the same time I would rather have them on one rack if they would fit.
4. I love brining and do almost all the butts that way. I put them in the brine and try to give them a good day but sometimes more and sometimes less.
Cook time? It's ready when it's ready. Sorry for being so vague but I have had some ready in about 7 hours to 20 hours. And I usually have the twin packs from Sams, about 8 pounds each.
5. You will do fine so do not worry.
I like to put my butts in around midnight and let them go until the next day. I have to work that into my daily schedule but it is easier to put them in late at night than to not have them ready until late at night and after supper time.