Do the apple store stock every configuration of Macbook Pro?

I'm considering buying a 13 inch retina MacBook Pro soon, probably 512GB, and was wondering what configurations apple keep in store? I've noticed that on the apple store you can configure MacBooks to have more RAM ext, and was wondering if all these are stocked in the stores, or would I need to order one online and take it into store? I'm really not the most tech savvy person, so wouldn't be comfortable setting up a new mac and transferring all my data over from my PC, so I'd need to visit a store for s omeone to assist me, and my nearest apple store is 100 miles away so I'd like to know they have the macbook I want! Also if I decide I won't want a configured one, just the normal retina 13 inch 512GB, am I just able to walk into store, buy it and have them move all my files, or do I need to make an appointment? Thanks for your help!

Probably in the wrong category sorry!