Disclaimer: I'm a member of the #develop core team, so I'm probably biased.
#develop should be a good starting point for you. It is written entirely in .net languages, has an extensible and resuable architecture and comes with a number of samples and tech notes.
I recommend you download the source code package to get started by reading the tech notes enclosed, then look at some addin samples, then the SDA (#develop for applications) samples. Some further reading might be "the book", however that is about an old version of #develop, so things have changed somewhat since that was written.