Hi Susan, You will need to determine if the wall you would like to remove is a load bearing wall, carying the weight of any upper floors and/or the roof framing. A load bearing wall will require an appropriately sized header to transfer the load currently being carried by individual studs to the fiundation. This header will result in a broken ceiling line which may or may not be an issue with you. As far as insulation is concerned, any exterior wall in the garage that is currently covered with drywall should be exposed. Then insulation can be installed that will correspond with your framing. 2x4 stud framing will only accept 3 1/2" R-13 fiberglass insulation, and 2x6 studs will accept 5 1/2" R-19. Fully insulate the cavities and install new drywall or paneling. Get a good quality slider or French door unit. The thermal effectiveness of better quality units will be appreciated. How do you plan to heat this space? Good luck.