you don't want to use a notched trowel. I wouldn't even worry about putting a thick layer of mortar on the board at all. Maybe smear (and I mean really smear) your mortar in a thin coat over the Durock, only doing a small section at a time. Butter each brick with a nice, thick layer of mortar and wiggle each brick onto the surface of the Durock.......don't get ahead of yourself, only smear mortar on small sections of your board at a time, so as to not let it dry out too fast.
That expanded metal, when impregnated with mortar, will not move at all once it sets. My hearth in the kitchen has NO board under it at all. I put down tar paper, built up a form in the shape of the hearth, screwed my expanded metal lath to the sub-floor, and poured 1 1/2" of concrete right on top of it. Layed my tiles right to the concrete with thinset mortar. No cracks, looks like I did it yesterday, and I did it almost 6 years ago.
No. You need mortar. Type S is fine.
Grouting is what makes the piece you are doing a solid unit, so yes....it will greatly strengthen the bricks. I hung real stone veneer on my walls, all through the house, and it is heavy stuff. Never lost a single stone, still tight as it was the day I put it on. And I used Type S mortar.
No, just spray right before you lay. not soaking wet, just damp.
That can be a problem. Only make your mortar the consistency of mashed potatoes. Too wet and the stuff won't stick right.
What percent are you mixing the type S with sand? I go almost 3-to-1 with my mix. Works fantastic.