I would think 8 oz per person if you didn't have the other items. As such 4 oz per person would be reasonable. I don't think you could go lower than that since everyone will want a good taste of that delicious brisket.
Exactly. I personally would lean toward 40# of raw un-trimmed brisket. Figure 4 large packer briskets. I am betting that in addition to the wings and drums there will be other sides and salads. You can always do 5 full packers and be sure you won't run out and have left overs. I'm one to not cut it too close and like to have more than needed. To be sure the brisket will be the star