I haven't used Mono, but I've been surprised at the sophistication of the projects are using it, and I hope to get an opportunity to try it out myself on a real project this year. When/if you get around to using the Roslyn assemblies, Mono is worth a look.
As far as using the .NET assemblies from C++, you'll need to use Visual Studio to compile the code that references it with the /clr compiler switch, but it's really not bad at all. The biggest challenge is to find an editor that understand C++ and .NET. Up through VS 2010, C++ has been an afterthought, without any .NET Intellisense. And when you've used SE to do a major .NET project, you'll know why I'm beating this drum so vigorously.
Looking forward to the SE improvements at this that I'm sure are coming, eventually.