Hello all, I'm looking to rebuild my hearth but having difficulty figuring out the best method. I've been given several suggestions as to how to go about doing it but would like to get another opinion from the experts here. Info on pic

• the opening you see with the plywood goes straight through to the basement
• close-up photo of the hearth shows a hole that goes straight through to the ash box
• will be removing the bricks and reinstalling them with new mortar
• the height of the hearth is two layers of brick
• two large pieces of slate originally sat on top of the brick
• the hearth is being replaced because it was poorly built and mice were living in it

methods of fixing

1. frame the opening with 2x10's to the height of the subfloor then use durock on top of the 2x10's with poured reinforced concrete with rebar up to the top brick
2. place 2x4's horizontal to the opening, place plywood on top. pour 4in of concrete up to subfloor, place cement blocks on top of cement level with the brick to support the slate
3. using rebar to hold cement blocks flush with the brick.

questions:

1. I believe the code states that there needs to be a thickness of 2in of flame retardant where the hearth is. is that correct?
2. is there any way of making the hearth level with the flooring? would it look dumb with the wood insert being higher?
3. I purchased a quadra fire insert (Voyager) not really a question
4. does insulated liner worth its weight and gold? the lady who sold me the stove said it wasn't needed where I lived. (Connecticut)