Fire Alarm Placement Assistance

We're in the process of moving our gas fireplace to a more central spot in our main living area.

It's an open floor plan and this room also has our kitchen and dining at the other end of it. The cathedral ceiling runs the entire length of the 33' room.

The smoke alarm was mounted on the wall within 12" of the peak of the ceiling. 
 

1. Inspector said he doesn't want it mounted on the chase of the fireplace due to dust intrusion from the backside, which seemed strange. Putting it on chase would also mean moving again if we chose to wrap fireplace in stone.

2. Inspector suggested moving off to one side of the chase, on the wall. That would put it below the 36" max from peak of ceiling measured down ceiling. 

3. We could put it in the ceiling in a more central spot, approximately 16.5' from the stove and fireplace.

Is that a bedroom door to the right?  Code comes down to "In out, up down."  Inside each bedroom, outside each bedroom, one on each floor.

I would place it above the exit/bedroom door nearest the ceiling but I'm no code master.  I error on the side of more is better and combine the fire and CO detectors.  The outlet plug in CO detectors at floor level are typically free if you ask your local fire department.

Will these be hard wired, making the decision permanent?  Or, will these be battery operated, very portable units?  

Hardwired.

If you haven't picked the alarms yet, I have a few of the Nest ones. I've never had smart ones before, but these network together, and have a motion detector as well. If the lights are out in the room and I walk through, they glow green and provide some ambient light. They don't light up for the cats which is nice. They are combo Smoke and CO2. There were 2 in the house when i bought it, I added 2 more with no issue. https://store.google.com/product/nest_protect_2nd_gen?hl=en-US&gclid=Cj0KCQjwzLCVBhD3ARIsAPKYTcQRFZKRmGd9jyMlkBs7_jrMjinCdipx0dQkjKNzbP6EasMQFly_7ggaAr0TEALw_wcB&gclsrc=aw.ds&pli=1