do u have to make an appointment to visit this apple store to buy a new computer and to have all the files, emails transferred from the old iMac to the new iMac?

The best way I will go about it is to purchase online if you know exactly what you want, and then you can pick it up @Apple store. You can set up an appointment after you make the order, and Apple will get you a specialist to help you.

If you're planning to do anything other than just make a purchase, you'll want an appointment. (File transfer is a fairly easy process though.)

Most likely yes the lines are long!