Craig,

These are some answers to your questions as far as I know.
In order,

1- They have always alternated between the planes and heli's
2- No. One flightline so the spectators and judges can have the best possible view of what is in the air at the time.
3- I'm not sure
4- I'm not sure
5- Without having the judging criteria in front of me I'll give you what I remember.
I am almost positive that a violation in the flightline is a ZERO for that round.
I also know that if any part of the plane touches the ground at anytime during a flight that flight is over.
(I think that is a change from years in the past)