Couple years ago, I bought a frame. Then I bought parts. Took me a year. You could do that, prob a lot quicker. Most of the small companies will give you 'a la carte' but it'll cost ya. The big advantage of a big company is you're getting a lot for your money.
What's the big deal with discs? I don't want the weight,and most brakes these days work real well. Can they work reliably in a commuting environment?