carbon stem is just a waste of money and it doesn't save weight either. a good aluminum stem (like Easton's EA90) is a much better value for your money, oh and in the case of Easton, it's lighter than their most expensive carbon stem. But in any case, stem doesn't matter, and if you're dead set on carbon don't listen to me. Get what you can afford, what looks good to you and is in the length you need.

As for bars, what matters most aside from width, (even more than whether it's carbon or alu) is the style of bend you want in the drops, the reach from the drops to the levers, and the height. Basically, it's a very personal choice based on your comfort and hand size, so it might be worth trying a few bars out at a bike shop, if you're willing to buy locally.

Personally, I like aluminum better for cockpit components, because the bars are the first things you whack if you crash or your bike just falls over for whatever reason. I don't want the possibility of my bars snapping as I descend 2000 feet over two miles to haunt me in the back of my mind. Secondly, I have found some very comfortable aluminum bars (Ritchey BioMax) that weigh a ton, but just feel right to my hands. I'm no stranger to carbon components, but I kind of think it's a waste of money here.