If it's true mahogany, no stain at all is needed. It would obscure the beautiful grain. Look at pictures of antique Chris Craft boats if you want to see some beautiful wood in it's natural state. If it's luan, it won't matter what you do to it.

I, too, love, love painted black doors!! Due to the colors in our home, we ended up doing dark brown/black doors (Pratt & Lambert Obsidian). I love it, although I still wish I had black doors. One day, when we are repainting the house, I will choose colors that go with black! So, to your question. I would do all the same hardware, whether ORB or brushed nickel, etc. I also would do all doors the same color. I went through the same process - thinking only the first floor with brown doors but I was convinced by a colorist to treat all interior doors with the same color treatment so all the doors are brown. I don't regret it for a minute! I really love the look. Here are a few pics - all hardware is brass, as that is what was here. I love the color but I am not crazy about the style. One day we will change them out. French doors: My den:

I'd go white.

If you want to keep your ORB hardware, maybe this link will help you find a color for the door. http://www.mariakillam.com/ten-best-front-door-colours-for-your-house/