The best hair for watercolor brushes is expensive "kolinsky," a kind of sable. But you can do quite well with inexpensive brushes made of synthetic material. You will know the difference by the price. A large kolinsky brush of the finest quality requires a bank loan. A similar size in synthetic material is about one-twentieth the price. I once purchased a large, top-of-the-line kolinsky which has appreciated so greatly in value that I am afraid to use it and keep it in a safe.
 
I use a flat brush one half inch across, and another small flat brush. I use these two brushes for the majority of my painting. In addition I use one or two round watercolor brushes in size four or five. That is really all you will need. I store them in a round toothbrush container together with a sharp pencil of medium hardness, such as an "HB" for doing the drawing preliminary to painting. I also use an eraser which retracts like a ballpoint pen, and is available in any art or drafting supply store.