Excellent post, jay. A few notes;
~ Layout all lights first, lightly scribe the ceiling. Run a laser to make sure your lights are all lined up perfectly with each other, and the wall. Relying on a wall/trim and perfect measuring can work but only if the existing wall/trim is perfectly straight. Crooked recessed lights look horrible.
~ use a studfinder to ensure none of your lights are going to fall on a joist, or right next to a joist. Check all cans as joists may not be on 16/24 centers everywhere.
~ finally, once the above two are done, I like to drill a small hole in the center of where each light will go and stick a glow rod thru at a slight angle, and move it in an arc that covers the depth/profile of the can, to ensure there is no plumbing, ductwork, electrical, etc. directly in the way of where the can is to be mounted. If you have an in-wall camera, those work too if the ceiling isnt insulated. Much easier to patch a 1/2" hole than find out the last of your 6 (or 8, or 12) can lights is directly under a damned 2nd floor p-trap or fart fan ductwork.
Once those three checks pass, only then do I take the can light holesaw bit to the drywall/plaster ceiling. Have drop cloths or a shop vac at the ready for blown in insulation that rains down once that 5+" drywall circle is gone.
If it were my house I'd flank the fireplace with 2 lights on a dimmer and put the other 4 lights on another dimmer.
But it's not my house.
But if it were your house, that information is paramount.