My favourite resource that I discovered a few years ago in a similar Ask HN thread: http://eloquentjavascript.net

> Where do I go?

You don't really need to go anywhere else (especially not into the vortex of looking for the best resource) to learn and be confident with vanilla javascript.

> ... and how hard is this actually going to be?

Well that depends more on you and your preference for learning materials. I studied a chapter a day (like 3 hours concentrated per day) and was done in 3 weeks.