Jack - VG Doug Fir would be a good wood for exterior use. And much lighter than W Oak.

I mentioned W Oak since it is local (?), excellent in exposure, and not too terribly expensive. But the threat of fire. I guess you can see what makes it and what doesn't from the extensive fires. Seems like overhangs are the worst contributors to a building's consumption.

I did not advocate a pretty or fancy door (both relative terms...), but simple frame and panel since that is the backbone of so much woodwork. The frame is there to establish the size, panels are there to fill in the openings and keep the critters out. Torsion box is more complex and will tend to bow during damp weather. It is higher 'tech' than frame & panel being of the late 19th C, while frame and panel dates back to about 1600.

Adding lumber to one side of an existing door for decorative purpose will work, but does little to celebrate one's involvement with the craft. Same with foam and plywood. It just does not speak well of a person's involvement with this marvelous material.