Other than online doc that is available, are there any other resources for plugin and app developers?
 

Can we get official workshops/training sessions? I think we are happy to pay for a session as well.

Our developer documentation here is the fundamental source for learning our framework, but naturally we encourage you to browse through the source code to be familiar with it if you are working to write addons for our software.

I'll raise your suggestion of training sessions/workshops internally for consideration.