I'd recommend getting a hold of a local Siemens rep to discuss things. Sometimes there are wrinkles to complicate things a little.
That said, all you need is Step 7 Basic (for the 1200). It includes WinCC Basic, for the HMI, which can also be purchased separately.
Your PLC should have Ethernet onboard, so connecting should be relatively simple. The Basic panels come in both ethernet/Profinet and serial/Profibus variants, hopefully you have a PN one.
If you don't have any of the parts yet, and this is your first time with Siemens, you may be able to get a starter kit, which is a bundle of all of them together.