IT's kind of funny that you are asking if the brooks looks good on a Mtn Bike because earlier people were asking if it was racy enough for a road bike.
I always considered Mtn Biking to be a little closer to old fashioned bikes... therefore the retro saddle would look great on one. ON the other hand,
some Mtn bikes don't even look like what i think of as bikes anymore....

You don't have to get one with copper rivets.. The leather look is gorgeous, kind of like Bentley cars with leather interiors..
You will start noticing the little "brooks" insignia on the back of random bikes. THere is no "type" of bike for the Brooks, it's simple a type of person. Someone who takes care of their undercarriage.

As for your other q's I will let someone else answer. My husband is getting a B67 for the front of our tandem so we will soon match!