Am I committing a Major Faux Pas if I mix Chromed hardware when I re-do my bathroom, Brushed Nickel for knobs/handles and faucets in my kitchen and Antique Brass hardware on ceiling fans and Door Knobs throughout my home. I live in IL but close distance to St Louis MO

Mix away You mix wood tones in a room, you can mix metal tones too.

In my living room I have brushed nickel drapery rod and Lamp. Fan and entry light(visible from living room) have antique gold (I think that is what it is called now). No one has ever been horrified and run out of my house... LOL Actually, it is not something you notice.

I prefer uniformity, but that is personal preference. We have antique bronze (oiled bronze?) fittings throughout the house. Makes things easier as well IMHO.

If you're buying new, I'd match as much as possible. I personally don't care but I'm sure that some potential buyers would not like the mixed look. If you're looking just to replace to sell, I'm not sure it would be worth the investment. Post over on the General Decorating or Real estate boards, there are realtors over there who might have a different take on it.