I have been in the Army, and am an Eagle Scout, and unfortunately, I agree completely with tango. Just because someone is a scout or in the Army doesn't mean they are experienced backpackers. But, it does mean that they probably are a slight bit more responsible.

My advice, and I think TomD said it, is to do a pre-check of everyone's gear before, and the day of. I would ban alcohol and anything else you feel necessary (like big cans of chili). Everyone signs a waiver, and agrees to the stipulations before hand. Also, if you do a pre-hike of more than 5-8 miles, that alone will weed your group size down without you having to do anything else. If you tell everyone that you will do what I suggested, I would be surprised if you have more than 20. Shoot, I would be surprised if you had more than 10 that would agree to no alcohol, smoking, a waiver, and then finish the 5 mile walk with all gear and still want to go. Personally, I wouldn't take more than 10 people.

Oh yeah, and this is completely my humble opinion, but TAC vests are worthless, even in the army. I NEVER wore mine in Iraq. The Army wasted a lot of money on that piece of junk.