Anecdote: the biggest thing I am learning now is just how much professional painters allow themselves to completely change their minds in the middle of doing a piece. I never thought this before, I thought everybody just knocked things out once they became proficient (and yeah, that can be true but not always), more often when I watch a video of an entire painting session they can decide to completely move things around, change the background, the mood, etc, and they are using physical paint, not photoshop.
Also in drawing, there is MUCH more erasing going on than I ever thought. It's true that some artists just work straight ahead, but I have never allowed myself to rethink things if I don't like where it's going. I make the mistake of abandoning works that I think are not going right, instead of fixing things which is a very, very valuable skill to develop.
Watercolors are pretty unforgiving in my experience as a beginner because they are transparent, and you have to be careful and plan things out in advance. I think there is a lot of technique to master there if you are learning on your own.
So you would want opaque colors, and you can get that with gouache + watercolor but more likely you may like acrylics.
Color theory is important. Take time to work make your own tests and color tables as you get used to a selection of colors.
I would add that watching videos of how different people work has changed how I view my own process. There are a lot of different ways to work and some may resonate with you.