I like mixing metals in general. Some people like to match throughout the home.

In your particular case, I tend to think of entry doors as a separate entity that gets its own treatment; choose colour to match exterior and hardware to match door colour and exterior metals. For your interior doors, you can go with a silver tone. Remember you will then have to change the hinges so they match :)

You might also then be thinking of whether or not to change light fixtures to match. I would suggest looking at lots of pictures with examples of mixed and examples of matched, and see what appeals to you. It's ok to live with a little wonkiness for awhile as your design progresses. For example, maybe the door hardware doesn't match the lights for a year until you can afford to update the light fixtures. That's OK, just be sure you have your plan in place. No more decisions until you know your end goal!