For paints, look at reputable brands and start with their student grade. It's often the same quality but with fewer pigments. It means that you'll have to fight with your paint more to get darker values. Watercolor is a relatively inexpensive medium, you can graduate to better paints later. You don't need more than 12 colors at first.
To start, find a style you like and search content on youtube. There is a ton of great artists sharing their knowledge out there with a wide variety of processes.
My most important advice would be :
- Learn the color wheel and how to mix paint (rarely use paint straight off the tube, it's often too saturated)
- Value is by far the most important thing to nail. It's the bones of your painting.
- Watercolor is one of the most difficult medium to master. It can be hard to grasp the technique while learning about light, edges, composition, and other painting standards. I learned my fundamentals in digital painting, which is much more forgiving, and would recommend it to anyone (you can find cheap tablets like Huion for 50$ and it works just as well as a 150$ Wacom). For digital, I can't recommend the course from Craig Mullins on Schoolism enough. He's not only one of the greatest digital painter out there, but a great teacher too.