Hi there!
I'm the author of the units plugin and wanted to overhaul my plugin for 2.0.0 to make it more configurable. However, the first version was quite "cramped together" and I still don't really understand the framework. 
I simply find the current status of the documentation confusing in many parts as some parts are written with skpm in mind and some without and I can't distinguish, which are for what.
I currently have the big problem, that all of my plugin's actions are run directly when Sketch is started.
Could you please have a look at my code (https://github.com/dploeger/sketch-plugin-units/tree/2.0.0) and tell me, what I'm doing wrong with the commands-files and the manifest. I just don't get it.
Thank you very much!
Kind regards
Dennis