flush hearth - suspended floor.

[diysos101]

HI.
My aim is to lay a hearth to be flush with LVT which will be laid over floorboards (9mm total).
It will be a 2kW fire with a permanently non-functional chimney, so no flush hearth regs issues apply and we will be able to walk by and use the space without stubbing toes.
Old house and he floor is suspended boards. Currently tongue and groove boards on a noggin support frame below.
Questions:
Thinking of depths: Can I take off tongue and groove, add a thinner (6mm) cement board to existing support frame then new hearth slabs to finish 9mm above boards? What thickness of adhesive will i need? This will determine the thickness of slabs i can use. May be black limestone pavers or a riven slate slab....
Back hearth is old bricks can I remove those and add mortar bed there. What is minimum mortar thickness?
Any other considerations or suggestions you can think of?
thanks

[moderator2]

Just one thread per topic please. I've deleted the duplicate in the building section.