My new favorite paper is Saunders Waterford 140# cold press paper, which I purchase in full sheets, 22" x 30", and which also comes in block format. Right now I'm painting on a 10" x 14" block. These are available from DickBlick).
I buy most of my watercolors online, usually from Cheap Joe's. In this current painting, I'm using two different brands of artist-grade pigments: Winsor & Newton Green Gold; Transparent Yellow; Transparent Orange; Winsor Blue GS; and from Holbein Brilliant Orange; Burnt Sienna; Opera Pink.
I did a light pencil outline of the three koi, and left white space around the fish so the colors will blend, wet-into-wet on the paper, and result in serendipitous shapes. I'm using a #12 Round brush.
The next stage is to add details to each fish. A wet-into-wet application of color makes beautiful runs and blossoms, and the advantage to using a watercolor block is that a painting-in-progress can be turned easily to encourage flow and blending. One of the three koi is nearing completion -- it just needs some scales.