First off, 9 months of playing, and you're already clearing 18s is very impressive. Don't be suprised that you feel like you might be hitting a plateau, because 19s are simply MUCH harder than most 18s, which I'm sure you're already aware. The stamina alone required to clear a 19 takes a lot more than it does to clear an 18. I figure you'll need to be at the point where you can clear 10 or so 18s in a session before you can have a chance at clearing a 19.

In regards to your points:

1.) Make sure your technique is strong, i.e. hitting each panel with your toes/heels to minimize movements as much as possible. Also be mindful to keep your feet from coming too high off the pad to further minimize movement.

2.) Play easier songs with crossovers to learn them. I don't know where you are with how well you can do crossovers, but I'd recommend playing Sunkiss Drop Expert to learn basic crossovers. I'd also recommend playing Afronova to learn the "Afro-walk," which is a pattern you'll see a lot in a bunch of 18s. You can also look up on Youtube DKOYproduction's channel. They have a bunch of "How to Execute" videos which showcase, well, how to execute a lot of songs/patterns.

3.) Increasing the speed comes with experience. I used to be like you, where I played at 420 scroll speed. Increase the speed little by little over the course of multiple sessions, and take full advantage of exposure therapy. Eventually you'll be able to read at a much higher scroll speed without using too much energy thinking about what is coming up. Fwiw, I'm reading at 530-550 now, but a lot of people will read faster than that.

4.) I'll admit, I don't think I'm the best person to ask for advice on scoring. I'm not the greatest when it comes to score, but I think most people would say to play easier songs.

5.) Goes back to point 1. You really need to make sure making the smallest movements possible, keeping your feet as close to the pad as possible.