It's because Windows Phone 8 uses a different flavor of .NET called .NET for Windows Phone which is missing some of the types available on other platforms. You'll have to either replace these types with different ones or implement them yourself.
Yes, it's UNITY_WP8.
It has to be changed both in Unity Player Settings and Visual Studio MainPage.xaml file.
All Windows Phone 8 devices have GPUs that support feature level 9_3 of Microsoft Direct3D 11. Higher or lower feature levels are not available.
No.
For that watermark you go away, you have to build the project in Master configuration in Visual Studio.
Page last updated: 2013-08-19