Glue and screw the 10mm insulation board down no need to use ply.. make sure the T&G boards are solid with no deflection. Put your wire on top then Self level over it, encapsulating all the wires.
i love a grouting tool.. 2mm joints and wooden dowel.. it gets rid of the air bubbles and pin holes. It also saves the use of too much water when washing down.. its so important to grouting still.
its basically render what they are stuck to.. sand and cement.. once you get behind it, it tends to come off easier.. just keep on plugging away with the sds. If one of the other lads know an easier way then cool. If not good luck and keep on going.