Well after you get the phone I'd start with getting a good case(never hurts to use protection).
After that I'd go to samsung's website and get the usb drivers for the phone. That way you can put all your music, and any videos you'll want to be able to watch on the go.
Finally I'd get launcherpro. This is far from required, but I just wasn't a fan of the touchwiz layout. Launcherpro is really easy to use and so far its worked without a hitch for me. Oh! if you switch to a different launcher, make sure to download homeswitcher. That app makes it easier to swap which launcher you are using. Its really good when you want to test out different ones.
Drivers:
http://www.samsung.com/us/support/downloads/SGH-I897ZKAATT click the software tab and download the usb driver.