A little guidance on existing metal form

[heating]

Greetings all, I'm hoping to get a little guidance prior to getting an install quote. From what I can tell I have a metal form (Heatilator or Vestal or K&W? no idea), not sure of the brand, and am looking at having an insert installed, probably BK Princess insert (but the wife has a say so who knows) as I'm familiar with the Princess stove from a hunting cabin and have been happy with it. Attached are photos, and it's currently been converted to gas. I won't be doing the install myself, but am trying to have ideas on what should be done before. It's about 25 yrs old and the previous owner didn't want to deal with wood anymore and said the room got too hot when they burned wood. Chimney is massive and totally inside with no exterior walls. All I know is the metal form is at least 3" thick as I can put my finger in at the fiber between the brick and metal and still feel it.



For the combustion air opening at the bottom (5th and 6th photos from two different directions, I'm planning on the installer tearing out / cutting the cover and damper as the floor is recessed 1 1/2" and It can't be in the open position unless the whole stove is elevated.
Insulated liner should be no issue as it's a straight run up although I was surprised a little to see a few feet of brick prior to the clay liner starting point but I guess that would have been based on the metal form's outlet size.
The two fans are only controlled by an on / off switch and the previous owner said it got too hot in the room, but if the insert stat works as well as the stove stat, I'm not worried, but I could always connect the blowers in series with a line voltage stat.
Ember protection will be needed.
Can anyone tell me how the metal forms are "sealed" i.e. how they actually connect to the brick? All I'm seeing is concrete at the bottom and block at the top openings in the face of the fireplace when I look in, and it's too cold yet for me to fiddle around with removing the damper & handle to try and get a better look at the top. Not the metal tubes as I've seen before. I'm not planning on burning 24/7 just weekends mostly.