With question number two.
Post frame garage door header.
Install the header jambs and center pad of the frame using a 2 x 6 lumber for the header jambs and center pad.
This would allow for a three foot space between each door and make for a much better target with a wide trailer.
Header requirement 2 at minimum the header should be 12 wide with doubled 2 4 at opening and ceiling running the width of the door with a 2 4 in the center of the opening for the center bracket to attach to.
Building a structural header for a garage door opening can be handled on the jobsite and will offer the same structural support as more expensive solid wood beams.
The procedure for constructing a header for 6 inch exterior wall framing can be modified for any wall thickness.
Attach lumber to the face of the garage wall to the edge of the garage door header.
You would actually end up with 20 inches of light panel above the door of which most of it will be blocked off by the top overhead door jamb the overhead door header and the eave girt.
Together the headers king studs and trimmers act as a system that transfers weight from above down and around the window and door openings to the floor and foundation below.
Most conventional garage doors are 7ft.
Cut a 2 x 6 piece of lumber and nail to the face of wall exactly in the center of the garage header.
Get a door with the same size as the one you are replacing.
Last pull a measurement from the top of the 2 x 6 piece of lumber that you just installed to the ceiling of the garage.
The longer the distance a header spans and the heavier the load it supports the more substantial it needs to be.
Header the header is ideally a minimum 12 wide micro laminated beam that spans the width of the garage door opening.