As much as I love CoffeeScript, it's not a substitution for learning JavaScript. CoffeeScript is basically just JavaScript with a prettier syntax and if you don't understand JavaScript you won't understand CoffeeScript.
That is completely true, you can't treat CoffeeScript as a replacement for learning Javascript in fact I'd say you need to have a pretty strong understanding of JavaScript to really use CoffeeScript well. That said CoffeeScript does some nice things to prevent typical small js errors for newer devs.
Very true. I love CoffeeScript very, very much. It's my favorite language - I like it even better than ruby, if you believe me! I like using indentation instead of stupid 'end's that only God knows are ending a loop or a def or something else, I like the use of ... instead of * (for splats), and a few other things.
But, as much as I like CS and hate (really hate) JS, I have to agree with you wholeheartedly. You must know JavaScript well. Variable/function hoisting won't bite you in CS, but other JS idiocies will.
Read Douglas Crockford's "JavaScript: The Good Parts" at least twice (and take a lot of notes). It's the best no-bullshit book on JavaScript (the language, not "how to use JavaScript in Node/front-end web design") around.