It mostly depends on what you want to do. Xamarin would be a great fit for cross-platform mobile applications, WPF(https://msdn.microsoft.com/en-gb/library/ms754130(v=vs.110)....) for big desktop programs and WinForms for tinkering with old software.
UWP is indeed the big thing for MS now, but it has lots of programming languages support(so not only JS)! I don't know anything like Sketch really; maybe this will help https://developer.microsoft.com/en-us/windows/apps/design
You should try VSCode(which is a lot like Atom, has excellent .NET support through OmniSharp) https://code.visualstudio.com/
C# is getting more attention because a lot of F# features got into recent C# versions, people not wanting to make the switch to FP and not getting full attention of MS.