Crown Molding Suggestions

My wife and I have been working on painting and improving our new house and recently we have painted our family room. We additionally, we are going to install the same crown molding that exists in the foyer. It’s a 3 5/8” standard HD Crown Molding in 8’ lengths the room measures 17’ by 17’ . However, I’m not sure how I should install the molding. I have a list of potential issues.

1. The ceiling in the room is 18’ (feet) tall and I only have an extension ladder.
2. I do not have an air nailer.
3. The stone fireplace goes all the way to the ceiling.

Here is a quick picture (after it was finished and painted):

My questions are this:

1. How do I attach the crown molding to the ceiling while working on an extension ladder?

My thought process is the make 6” wide backer boards (shaped to the 52 deg angle of the molding) and place about 4’ apart nailed to studs. Then nail the molding to the backer boards and cock the joints. I’ll nail the center section first and should be able to reach each end from the ladder.

2. What is a good way to work around the fireplace? Stop the molding at the edges or mold around it?

My thought process is to stop it before the fireplace since we are later going to add recessed lighting to the front of the fireplace or perhaps build and overhang that would extend about 16” out from the wall to hold portion of the lighting.

Any sugesstions?