First, a comment about your wish to tour DMZ. During one of my visits to Korea, I wanted to tour the DMZ area and asked the hotel concierge to find a tour for me. Due to the short notice, no Korean tour group was available BUT he found a USO tour to be available. I found out later that the Korean tour does NOT go to all of the places the USO takes you, so do that rather than driving up there by yourself.
As for other places, what I would do is look for few interesting places you'd like to visit using whatever guide you can. You might ask here for the suggestions. After you've decided on the places, use public transportation to get from one place to the next but hire a cab on a daily basis to get around the area. You can probably hire the cab to take you places AND have the driver act as a guide. If you don't speak any Korean or the cab driver doesn't speak your language, that could be a major problem BUT I think this will work out better than having you drive around the country looking for places to visit and things to do. I think you might get lost more than you planned, then the two week trip will be something you'd wish to forget rather than remember.
Good luck and have fun. I wish I had the time to do what you are planning.

Hyunja