Stay away from GameSDK. It's gonna get completely deprecated soon. And you will stuck on some certain Cryengine version. And also GameSDK is very messy, it's like trying to build game on the top of the other game. With massive amount of useless code. Build your game from scratch, using existing components, build your own components, you will be grateful when your game will become very clean, modular sandbox that you can manipulate easily.
Cryengine tutorial videos on my Youtube channel! Check it out !