>>5781013TL;DR: 1 or 2 good quality paints (blue/brown), any kind of well mastered brush, good quality paper or learn to use poor quality paper.
First, paints: work mono-chromatically, at best with color temperature (ultramarine blue and a deep brown, both relatively cheap, yet permanent). Once you've got great results with that, you'll be able to invest more without hesitating.
If you can, pick them artist grade. If you don't, then try to use pigments like phtalos, or impermanent yet pungent pigments: phtalo is a mess to use with oils, but for cheap watercolors, its natural strength is quite handy.
Second, brushes: I've recently acquired a cheap (~4€) huge Chinese brush, a mix of goat & synthetic hairs, that gives me gorgeous marks. My Kolinskis can't even compete, despite being much, much more expensive.
That is to say: learn to use your brushes, their strength, weaknesses. Expensive brushes definitely have their uses, but they can't do it all.
Third, paper: 100% cotton paper usually is better. Still, two different 100% cotton paper will behave differently. If you can buy them on sale, then go.
Otherwise, you can try cheaper alternative (thick bamboo, cellulose papers). You can achieve great results with them too, but it's harder: the paper will have a tendency to dry unevenly, so you will have to manually balance this, while things work (more) automagically with 100% cotton paper.
