you will get the unreal script sources of the game (most likely, talking from experience from other TWI titles).
Unreal Script should be close to C++ for you to feel comfortable.
The SDK will most likely come with the HoS incarnation of the Unreal Editor for creating maps. Beside that, as i said, the UScript sources, possibly tutorials/example maps.
For coding you can chose from the generic text editor with UScript highlighting interfacing the compiler, nfringes UScript add on for Visual Studio or wotgreal.
Though i coded for CC with wotgreal, i moved to VisualStudio for a HoS project. In that other thread in this section there is some feedback about the different editors as well.
