You don't mention where you are from and what your availability of different types of meat is.This can be a decider.I try to stay away from catering ,as it will make you old.
I have been forced to work with some guys that think it is fun to do for a living.
This is not a direct answer to any of your many questions,but Elizabeth has helped many of us get our plan started.
http://forum.cookshack.com/eve...1028883/m/4221007444
Another forum member's small party.
http://forum.cookshack.com/eve...111055344#5111055344
This from another long time forum member.
http://forum.cookshack.com/eve...061040714#9061040714
To get more ideas,you can go to the pros forum,go to find at the page top,and enter "catering portions".
A couple things I've learned is depending on age of kids they fill up on chips and other junk.Breasts are the most difficult to cook and hold.Hot dogs and drumsticks often do a better job.
Cooking and handling four meats can be tough for experienced cooks with lots of gear.
Brisket can be difficult to cook,hold,reheat,and serve.
If the smokette has a weakness that takes a little extra to overcome it might be ribs.Many folks finish them on a grill to get them just right.
Some folks might do pork butts which cook,store,reheat,and serve well.
You can toss in grocery store smoked sausage for another meat.
Use the grill for legs and thighs the morning of the party.
You're talking 50 lbs each of pork butts and brisket-if you aren't talking pork loin.
This should give you some more ideas and we can answer some of your more specific questions when the real pros get here.