I have replaced all my doors except for the bathroom door with 1/2 inch birch plywood.
I intend to do the bathroom door when I'm home for the summer. It looks rather easy to replace except for that piano hinge with all it's screws. The front molding looks to be screwed on thru the rear molding.
Since the door is so large using 1/2 inch plywood may require a stiffener or two.
I did not treat the edges of the birch plywood other than to urethane the birch. Pictures can be seen under Modifications/Preparing a 1991 Scamp
16, it should be near the end of a rather long post.
I like the looks of the birch over the standard doors, it's inexpensive and easy to work with.
As to the side molding I would simply use similarly dimensioned urethaned pine.