Doors can be tricky, just make sure things are plumb. Take the door off and shim the bottom of the for the head to be level, then shim /plumb/nail the hinge side. You can put the door back on then to help keep the gaps on the other side consistent.
I would stain the door in a garage. Stain, poly, scuff with fine sandpaper, wipe off dust with tack cloth, 2nd coat of poly