Replacing / refastening fireplace hearth and back panel ?

Hello All ,

Can someone please advise me on the proper procedure for replacing a inset real flame type gas fireplace hearth and back panel (marble type )

Is the correct procedure as follows .

1. turn off gas to fire (disconnect as necessary)
2. remove the fire surround
3. remove from the wall old back panel
4. remove old hearth
5. make good surfaces ( one coat plaster etc ) clean and level hearth floor area .

The bits I am not sure about are as follows

what do you lay the hearth on (mortar I am supposing ) is it a full bed or just enough to bed the hearth level on ?, what is the mix 5 to 1 ?

how do you fasten the back panel to the wall ( liquid nails ? ) or some special adhesive ?

Do you have to remove all the fire from the wall or can you remove the old panel etc and just slot the new one into its position ?

Do you have to silicone in the fire back to the back panel ?

Thanks in advance for any help and advice .

Glenn