Are you able to get packers,or are you cooking flats?
Flats yield a little better,and are easier to handle -if you don't do much brisket.
Is this the only meat?
Jack's figures are pretty close to my guess for a mixed crowd.
Are all these folks bbq eating adults?
High school boys,or working men,might require a raw lb/person.
Kids may not eat it,so a pack of hotdogs thrown in is nice.
Wood is subjective,but 6-8 ounces should handle it.
Although you can do two large packers,I'd consider three 9-10 lb ones for ease of handling,serving,etc.
I'd cook them on your center three racks.
Hope this helps a little.