Feeding a large group

[Redneckinthecity]

I'm working on feeding a large group (about 100) with pulled pork and ribs.

I'm figuring a yield of about 55% on my butts, about 75% of the people eating pulled pig, and 25% of those eating pulled pig having seconds.  I'm using 1/4#/person to calculate. - So, I'm thinking to get the 23# of finished cue, I need to cook about 42 pounds of butt.

Where I'm having trouble is on the ribs.  Guessing 50% of the people eat ribs, and 1/3 rack a person for those who do.
Is this a safe assumption?  16 racks?

What I'm planning to do is cook my butts ahead of time in my BDS, and do the ribs on my big rig. 

Any advice on cooking the ribs?  Since I can't do my usual smoke in BDS/aluminum pan in the oven with apple juice and foil/gasser to crisp method, should I plan to cook the whole time on the big rig and plan to mop frequently?

Thanks to all.

[Habanero Smoker]

I do a couple of cooks a year for groups of around 30 (mixed adults, teens and younger children). When giving people a choice, I find that more ribs are consumed during the event, then pulled pork.

If you are using your big rig to cook the ribs, you should go over the the The Amazing Rib Site which would be more helpful.