The only gripe I have after a quick read through, is the one which every now and then bugs me when I call a Templater template: It needs an active editor. The template doesn’t need to change anything related to the active note/editor, but it needs that instance to be able to execute any template.
I’m not exactly sure where this requirement isn’t met, but I believe the most notable is if you’re in the New tab window with the message No file is open. I’ve tried (a little half-hearted) to find a way around this, but haven’t found it yet.
So I endorse the work you’ve done, and I will come back and look at some of the details related to particular QuickAdd actions, but I just wanted to raise a little awareness of this active editor issue to insert Templater templates.