Is this capped at a certain number?
Not specifically, but from my end personally the smaller the group the better. With 5-6 people I could give everyone more help and individual guidance; not so much with 10 people.
Also for the hiking part (which is most of the adventure, after all), I'd think that smaller groups would be more efficient. Imagine 10 people trying to cross one of the major rivers, or on one of the 6-inch wide stretches of trail...
Just my $0.02.