New coal stove hearth, hardibacker, please tell me what you think !

New member here but long time reader. After extreme frustration on finding solid information on building a hearth & wall protection for my Alaska Kodiak 100,000 btu nut coal stove I came up with this idea. The construction is steel studs, two 1/2" layers of hardibacker screwed to the steel studs with fire caulk on joints, topped with ceramic grouted tile. The size is overkill, the actual floor protection im not so sure about. Please tell me what you think. Also please check my piping, i just did a barometric damper with two 90 elbows, i feel like im missing something. I also did a little science experiment because there seems to be alot of debate about hardibacker vs cement board, i put a torch directly on the hardibacker for 35 minutes, im confident that it will never catch on fire but not so sure about the heat that radiates through it. Its built now so maybe this is late but i want to make sure im not doing something really stupid here before i fire it up.

thanks for all the comments, this was actually the first time i worked with ceramic tile im very happy with it. Yes i have checked on Nepa, there is alot of good info there too but wasn't exactly what i was looking for. The pipe is only 14" from the ceiling, since posting photos i have added a sheild over the horizontal part of the pipe. The thimble was here in the house before i moved in, its a 6"ID round terracotta pipe with appears to be some type of concrete around it, that goes into a cinder block chimney lined with rectangle terracotta pipe so its not perfect but its not drywalled right up against the pipe like the photo appears to be. Insurance company gave me the ok, but only via photos they never came out.
I'll put some more construction photos up here. The studs are screwed to the wall and floor with drywall screws, the studs are screwed to each other with self tapping modified truss screws and the hardibacker is screwed to the studs with cement board screws, im pretty certain it is not going to move. Each layer of haridibacker was caulked with 3M fire block and I made sure each layer had joints in different locations and there was at least one full peice of hardibacker under the stove. You can see the old beast of a stove that was there probably since the 40's ?, it was sitting on a pad made of wood with a peice of sheet metal wrapped around it almost the exact same size of the stove, that was it, there was no other ceiling or wall protection.

I actually wanted to use the old majestic stove that was there, but the insurance company said it had to be UL listed, ha- im pretty sure that stove was manufactured before UL was invented. The insurance company (erie) told me they have been having alot of problems with fires because of people trying to heat their homes in a poor economy with old stoves or inadequate floor / wall protection. The 14 clearance sucks, but moving the thimble would be a nightmare im sure. The standoff brackets are only about half way up, there is wainscoat board on my bottom 36" of the wall, so instead of removing it i just compensated with the brackets on the sheetrock, I was trying to be non-invasive.