I took the Beginner level class and I greatly enjoyed it. It's not specifically about Blender (there's a lot of content on cinematography) but that is the primary application used. I went from 0 Blender knowledge to making this:
Not what I would call a great image or anything, but I'm really happy to learn that much in a month.
By greyboxing you just mean placing generic shapes around and rendering it for use as a base? It would be fairly easy to pick up, though I did have to change the viewport controls to emulate Maya since they were irritating to me. You might have to block out a day to learn where all the UI stuff is though.