I planned to get rid of my garage door and put in a wall/ window but in the end put the brush-type draught excluder around the sides and top and a rubber strip along the bottom, and filled gaps around the frame with expanding foam (there's still a small gap at the bottom which means air can get in to avoid damp problems). I covered the door with sticky-backed soundproofing insulation called Thermoliner - it sticks really solid to the metal, reduces sound that could annoy neighbours and reduces heat loss (I also did the inside of my van with it - which is what it's sold for - it works very well). Also, having a garage door means I can open it some when I'm done sawing etc and air moves through both top and bottom of the door (I also open a window) meaning quick change of any air with dust in it. I'm now glad I didn't replace the door.