How deep should I memorize lines of the Sicilian Dragon? How deep should I memorize lines of the Sicilian Dragon?
1400s USCF
The Dragon seems to resonate with me the most, after looking at all the variations. Do I need to get a book on it, or can I get by by just watching YouTube videos, looking at games, and experience?  

There's a guy on Youtube, that has like 20-25 minute videos on each of the four main variations of the Sicilian Dragon?  Example video: https://www.youtube.com/watch?v=VDRoBnL1gRg

Can I get by on just watching his videos, just playing it (and checking where I deviated afterwards), and playing through master games of the opening?  First memorize the main variations like 10-15 moves in, and then as I gain experience, learn the sidelines?
As someone who recently got out of the 1400s, I think it's much more important that you figure out where you want to be developing your pieces and why certain pieces are good in certain places. When I went about memorizing a bunch of moves, I very often (then and now) played people who would do something I'd never read up on.

If instead, you learn some of the reasons and/or general plan for a given opening, I think you'll be better off in the long term.