The good news is that it should be shown most nights whilst you're there. Keep your eye on the hours closer to the time and, if it's scheduled twice on any given night, that's a good option as the later show will be considerably less busy than the earlier one (that also applies to SpectroMagic at MK).
CMs open the gates around an hour before showtime, but people will start queuing up to an hour before that. Being first in isn't actually a benefit because you're likely to be shepherded to the far left and front. Not only will your view not be great, you'll be the last of 9,000 people out at the end!

Having said that, once you're in the auditorium, you can easily hang back until they start filling the seats in the area you want to sit. There's plenty of open space at the rear of the seating areas to do that. Ideally you want to be in a fairly central position, although I wouldn't get too hung up about that. Do make sure you're not too near the front, though.
If you go for the dinner package, you'll still need to be at the designated meeting point 45 minutes ahead of the show. The far two right-hand seating sections are reserved for those on the package, but they won't hold the seats once the main auditorium fills and, as that's likely to be around 30 minutes before the show, you'll need to make sure you're on time.