We have different kinds of doors in our newish home. All are the same wood and stained the same though. Most are six panel, though one is a six panel bifold with the flat areas painted in chalkboard paint. That's our pantry door. We also have a bifold door on our upper level laundry room. It has two lower panels with the top panels being louvered for venting. I don't know if that helps you are not. Do you have a floor plan you can share and show where these different doors are? I know Victorians use to do their private areas with simpler materials to make it possible to be able to use more extravagant materials in their "public" areas for show. Is that what you are hoping to acheive? I know we've thought about not taking the time to route the trim (we're still finishing our home) on the upper level to save time. It's more practical.

Interior trim or exterior trim? It may also help to post drawings of the design and what the trim is like. WARNING: Posting your entire floor plan opens you up to facts you may not want to know, but should. Be prepared for suggestions that will make for a better design. Keep a thick skin, open mind, sense of humor, and a glass of wine within arms reach. You may not enjoy it, but everyone else will and you will be better off in the long run if you heed well the advice.

Most exterior doors are one color on the outside and another on the inside. Yes, I would match your panels, in the Dover white.

No relation to each other, as door knobs are interior hardware; bathroom faucets etc are interior fixings (permanently secured). You can choose any finish you want for the bathroom. The bathroom door, will have black hardware.