To add to Jared's excellent suggestions:
Use C# rather than VB.NET. Most of the tutorials and source code uses this. Going from C to C# shouldn't be difficult. Whatever you do don't try using C or C++ directly COM interfaces are very difficult with these.
In addition to the sources that Jared mentioned there are the ASCOM platform sources on SourceForge. DriversandSimulators\OpenWeatherMap has an Observing conditions driver that reads JSON using JavaScriptSerialiser. That may give you a few ideas.
Chris