cheat the hinge gains on the door higher on the door so the entire door hits along the header but have the door as close to the opening as possible. a door should always have 1/2" clearance from the floor on the bottom, 3/4" for a closet door so to allow air flow
Standard doors today are 32" and 36" wide. 34" wide doors were dropped years ago. Before you cut a 36" door down, be sure that it can be cut. Nothing worse than cutting an inch off of both sides of a door and not having a solid stile left. 34" doors can still be special ordered, but be prepared to pay $$$.