Thanks for the feedback guys. We ended up going with the textured ceilings anyways (partially to hide some minor imperfections too. Here's what I learned:
What type of consistency should the topping mud be? Runny? Thick?
This varies depending on the type of texture you're try for. More "subtle" textures like Orange Peel require thinner mud topping. For my purposes, the ideal consistency was "thick paint".
What techniques should be used for actual spraying? Top-to-bottom? Left-to-right?
There's no perfect way to do this and it depends on the type of topping you're putting on the ceiling. For my purposes, a circular movement worked best. Again, your mileage may vary.
What preparation needs to be done beforehand? Taping off outlets? Placing plastic over windows?
All of the above. You essentially want to protect as much as possible and ONLY leave the ceiling exposed. We lucked out in that we're going to remove the carpeting so we didn't need to place plastic over the floors.
How full should the hopper be filled?
Follow the manufacturers guidelines on this one. Our hopper manual said anywhere from 1/3 to 2/3. I stayed closer to 1/3 since it got heavy after awhile.
What can we do if there are mistakes?
Practice beforehand. It's ESSENTIAL. If you do make mistakes though, quickly scrap off the area. Keep in mind that even if you use pre-mixed mud, it will dry a LOT faster since it's thinner.