John in NM
Double doors are more difficult to hang if you don't have experience with doors. There are two ways to go about any door hang - get the jamb square and plumb, then hang the doors, or approach it like installing a prehung system where the doors are already assembled in the jamb and the jamb is tweaked until they hang well.
I've done it both ways and each has its advantages. The main thing with either one is to accept that you're going to have to keep fiddling with things to get it all right and derive patience from that knowledge.
Can't help with laminating, cores, and all that. I've only built frame and panel doors from solid wood. I have built arched jambs by laminating 1/16" veneer on a form with clamps. It works as well as a bag - if you do it right. Got to build both sides of the form to distribute clamping force as evenly as possible.
Exterior doors are tricky to get right, and paint is probably the best solution for the outside - anything else is more of a maintenance headache than is simply repainting as needed. You can enjoy the varnished wood on the inside where it doesn't start looking like crap within a couple years.