- good pigments: nothing is worse to lose interest than using low quality watercolors, you do not need a large number of colors, but want then of good quality. Cotman is a good choice, but there are -depending on your location- professional grade watercolors of exceptional quality at most affordable prices (like Sennelier Aqua Mini) I started with a small Cotman field box and that's still the heart of my watercolor adventures for over 30 years now. When the Cotman pigments run out I replace them with professional grade Winsor & Newton pigments.
- good brush: you do not need many, two or three are enough, a thick, a middle and a thin one, and they do not need top natural hair, there are excellent synthetic brushes with "Kolinsky imitation" taklon bristles that are within anybody's reach, again it depends on your location which ones will have best price, mind the brand, nothing is more frustrating than a brush that loses bristles Despite having a quiver full of brushes, pens, waterbrushes, etc., I find that I almost always use only one single dagger stripper. Yes, I can use all kinds and sometimes use others, but honestly only one (and not expensive either) is enough if you learn your tool's capabilities. BTW, I originally learned on Sumi-e brushes, which are essentially pointed rounds and highly versatile. You can paint credibly with cheap hardware store paint brushes too, if you really want to.
- good paper: the motto goes 'life is too short to waste on bad paper', and it certainly makes a difference, but to start with, you can find affordable papers that work, just mind the brand -or look the reviews-, Canson, Bockingford are well known, but to paint small, cheap (4-5$) pocket Talens Art Creation 90lbs/140gsm sketchbooks have worked good enough for my quick sketches, I mean, it is not ideal, but you do not need to break the bank either to get started. Having tried many papers I'm in agreement. I'm not a heavy water user nor a scrubber, so more papers work for me than not. But I love Bockingford papers, Arches on the expensive side, yet some Strathmore or Canson postcard or larger sized pads work fine for most of my work.