What is the best way to host fixtures to a sloped ceiling? Are reference planes the route to take? How do I reduce the wait time when a model is opening? Should I audit a model when opening?

I have a question for you first. Are you hosting to the actual ceiling in the model, or is the ceiling part of a linked model? If linked, you have to go the route of reference planes. Just as you can't copy/monitor ceilings, your ceiling hosted families won't host to a linked model's ceiling element. If you are working directly with a ceiling element in the model you are in, your family should be a ceilng based family, and it should take on the proper plane from the ceiling. Another fix is face based families which are much more flexible in where they can be placed. The way the family is constructed will determine how well it works in any of these scenarios. placing a face based, or ceiling based family, will slope with the face or ceiling, but it will not hang properly unless the family can be manipulated to do so with proper parameters. I hope this answers your question. A word of caution. When you are creating section views for family placement, delete them when you are done. They can clog a model and are unnecessary. I used to create one section and then just moved it around to fit my needs. Less clutter that way.