how many venues will allow set-up before 3:00 on friday?
I believe that tournament would be scheduled during many school districts spring break. I can only speak for our club but we could be set up well in advance of that time. I'm sure the same would be true of other clubs/facilities as well.
i know in d1, (probably worse in d3/d4), that it would force parents to take kids out of scholl friday to be there on time, weigh in etc. do we want to lose any more school time than we need to? this sport has a bad enough reputation for that anyway.
See my above answer but beyond that many parents don't mind taking them out of school for Tulsa et.al.
do most venues have the room for such a big tourney?
I believe most schools with two gyms could handle such a number in a split tournament and particularly with the 16U being wrestled off on Friday evening.
how many families actually travel the night before for districts/subs? might not be as many there to watch as we think.
You won't get them all that is for sure. But if you get 30-50%? I would take that and it would be good for the local merchants and the host's concessions and more importantly good for our young wrestlers to get to see the big boys wrestle.
how would you charge admission?
I wouldn't, this would be no different than any other sub or district tournament with the exception of the 16U group being wrestled off on Friday night.