Study plan, best way to learn.

Yes. You should do all of the above. Seriously. The more you practice the more you will learn. As far as forgetting stuff, it is natural so you should not learn different things at once or you will get mixed up. When you need to, you can have a reference sheet to remind you of syntax. I learned C, C++, Java, and now Swift. There is much overlap, so you just keep getting faster at learning. Some small differences but basically lots of common ground.

I'd definitely do some of what you're describing.

If you're a note taker, and on a Mac, I highly recommend Quiver for taking notes. It makes taking programming notes really easy. For instance, you could have some notes on a JavaScript concept and below the notes Quiver gives you the ability to write pertinent code.

Give yourself some projects to do, as well. The best way to solidify information is usually by doing. If you want to use a certain CSS property, try to remember if off the top of your head, but look it up if you can't. Next time you want to use that property, you'll probably have an easier time remembering it.

When you're done with the JavaScript stuff, brush up on CSS a little.

Hope that helps!