Hi Manuel,
yes, the Tobii.EyeX.Client dll is absolutely necessary for the eye tracking to work in your program. It’s a native dll, not a managed assembly, and therefore it’s not possible to just add it as a reference to the C# project. You can add it as content instead and have it copied to the output directory as part of the project build (“copy if newer”). You can find it in the libs/x86 directory in the SDK package.
A more comprehensive post on how to set up a C# project will follow shortly, but in the mean time I hope the short summary in this thread can be useful:
Project building with several errors when using EyeXFramework
And yes, the Start method used to be called Init in the earlier versions of the framework. Did we miss to change it somewhere?