I am a little concerned about the stock of the iPhone non-preorders. Does Apple set aside a large portion of stock for people that do not? I am a little worried that a store would only have a small handful of units due to the majority being fulfillment of preorders.
Yes they do set aside a lot of stock. There are a lot more people that want a phone than there is stock on launch day. You should worry and show up where you expect to buy the phone earlier than "the other guy". Read the 1,345 other posts about this for more info.
They usually have at least 10-20 liters of phones for walk-ins. You should be good as long as you get there early.