I just finished installing the Inferno heater yesterday. It went pretty well, minor hiccup with one of the gear clamps. The heater is a very tight fit in the dash, but it is a clean looking install. I took it out for a little test drive and the heater is functioning.
For the doors I have rough cut the abrasion resistant lexan, I have seals and barrel fasteners on order and I have 3/4" square tube that I will make the frames out of. I will get after it boxing day, I hope.
My thoughts for a window that opens is this, I make a fixed window set up first. If it goes well then I will look to make a slider window that can let in more air. My windshield can open so can always get air that way. I plan to remove the windows from spring to fall as the cab would be a hot box when closed in.