I can only speak from my limited experience with Infusionsoft so hopefully other VAs with more extensive experience will chime in! I found it very frustrating, and I'm usually very quick with new software. At the time I was using it the backend was just not at all intuitive or user friendly.
It has some very powerful features though and is pretty robust - function seemed great, form - not so much. Maybe it's been updated since then... I'd certainly hope so!
I don't have a course recommendation but hope my response will bump your thread and bring more answers!