I recently built a wooden barn with 2 sliding doors 10' wide and 12' height. My question is how to best seal them off more so air doesn't come in and out? This is a new wooden barn made to look on old style. Doors are on top track and bottom tracks as well.

No easy solution that I know of. And in the north, the bottoms will ice up and be unmovable. You can tack on rubber 'garage weatherstripping' but it won't last long with all that friction, and will have to be at least double in thickness.
I assume that barns aren't meant to be air tight so that hay won't spontaneously combust?