Should a beginner move from fundamentals to opening theory? After learning the fundamentals, should one start learning openings or should there be something else in between?
Moving from fundamentals to memorization of openings is probably not recommended. I would instead recommend learning the fundamentals of openings (controlling the center, developing minor pieces, don't bring out the queen too early (usually), pawn structure), and then, as you say in your comment, focusing on tactics practice.

If your goal is to play fast games, then studying openings is certainly going to help you increase the speed out of the gates. 

If your goal is to improve your slow game, which is probably a good idea for most beginners: my recommendation is to consider each opening move as carefully as you would a move later in the game. Many openings are as tactically tricky as the middle game, so it pays to be careful.

Just my opinion. Obviously, there is a point where learning some openings will be helpful.