On the rebar, in my garage floor, they pounded rods into the compacted base and suspended the rebar lattice above the base about 3", the floor is 5" thick. I can't say enough about maximizing the available R-value available. I optioned for the highest R value the building could hold, my actual heat requirements are less than half of what was originally calculated. It was supposed to need 160k btu on the coldest of days, but one 80k btu/hr tube heater does it with ease. I would also take the wall to maximum height with a high lift door option.
Edit: the liftmaster remotes suck balls, short transmit distance,but the buttons are too easy depressed when in your pocket. My old opener needed a solid push to "click" the button, the liftmaster swithes activate with little pressure so the door starts doing things if you lean against something or bend down.