I would get a complete bike and ride it for a while. You'll start to figure out what you like and what you want to change. I'm 6' and around 200 lbs, and I've been riding a Jamis Beatnik for a while now and like it. It's nothing special, but it is cheap and will get you going. After about a year I replaced the pedals, bars, and saddle and find it comfortable. For what it's worth, I'm not a huge fan of the blue 2015 Beatnik. So bright.

edit: you'll also want to think about the other things you'll need to buy. you probably want a lock and helmet, so if $600 is your total budget, you don't want a $600 bike.