Thank you @ysc for your cool and detailed documentation and of corse for the new impressive UI! 
Your documentation helped me a lot to get started! Something where I needed extra information was on integrating my own custom icons in the new main UI.
Luckily the community forum helped me to find the solution. I wrote the workflow down and I thought maybe it is useful for others, when they start building their own main UI widgets and crafting / designing their own icons.
I hope this “self” advertising of a community post is welcomed. If not, please let me know! Thanks 