Anyone know of any good resources for getting up and going with Visual Studio Extensibility (tutorials, etc.)? There seems to be little around the net as far as I can see. Or mayabe I'm just using the wrong keywords in Google.
What I'm generally having trouble with, at the moment, is navigating through a solution and accessing code files.
Not sure what you mean exactly by 'code-model'. A good place to start is MS VSX learning center. A complete chart of the exposed object model is here. There's also a chance that what you're after is FileCodeModel, in which case you can google it directly (or alternatively ProjectItem.FileCodeModel), and you'd get many examples and references.
Here's a fantastic resource with a ton of HOW-Tos: Resources at MZ-Tools