I think 6 might be tough. You could easily do 4 though. Four butts is still quite a bit of meat and may be enough for 50 people. Otherwise, I would do 4 in one smoke and another 2-4 in another smoke. Pulled Pork reheats extremely well. For serving such a large group, you could reheat in an electric roaster or large crock pot/s with some apple juice for some added moisture.
For this much meat mass, I would smoke at 235-250 degrees and make sure you place the bigger butts on the lower shelf as they will get more heat than the upper ones. I would try to probe 1 bottom butt and 1 upper butt assuming you have a multi-probe thermometer or multiple thermometers.
Do you have a Sam's Club Near you? They have Bone-In Butt two packs that I much prefer over the boneless ones. For the boneless butts, you are going to want to string them together so that they smoke as a larger mass/piece and don't fall apart when you remove them.
I love the boneless butts for when I make buckboard bacon, but for pulled pork the bone-in butts (if you can get them) are a better choice. If not the boneless from Costco are very affordable and very good cuts of meat.
This sounds like a fun project Don. Let us know if you have any further questions.
Also, I almost forgot to give you a big welcome to the forums from ND! Did you just get your smoker, or are you just new to the forum?