Newbie here and need help with questions
If you are burned by the attitude of 'pros only' forums, no need for pretense here - this is, after all, DIY chatroom. So, if 'the hire' is your husband just say so.
Otherwise, if the hire is a pro, he should know what tile/grout/etc to use.
And some answers:
1. Grout. If by 'kind' you mean sanded vs unsanded, it depends on how wide you want the seams. Anything over 1/8" is sanded, 1/16" and below unsanded. This being fireplace and all, I'd say light shades of grout are not prudent.
2. I'd say either works. Backerboard is probably an easier solution unless your hire is a pro at floating mortar.
3. IIRC, minimum distance from the fireplace floor to combustibles is 46".
4. That would greatly depend on the tiles you select and your model of TV. I'd probably top the tiles with a thin narrow black granite mantle hiding the drywall edge and then mount the TV about an inch above that.