To speed up development with Commerce Engine customisations, I have created a library of templates for Visual Studio. This should remove the necessity of referencing the sample commerce engine plugin project or decompiling and cleaning code from certain DLLs just to get to a starting point for your customisations.
The templates can be installed in Visual Studio via the Extensions and Updates or by downloading it from Visual Studio Marketplace: Sitecore Commerce Engine Templates.
Source Code: Sitecore Commerce Engine Class Templates