Watercolor paints are labelled professional grade or student grade. Professional grade paints are definitely stronger colors and are easier to achieve gradient washes. The tube paints really helped me become more comfortable in blending colors. We only used 6-7 colors and no black or white. Our basic colors were: Lemon yellow, Gamboge, Ultramarine Blue, Prussian Blue, Cadmium Red, Rose (AKA Qunacridone Rose, Permanent Rose) Yellow Ocher, Burnt Sienna. We blended everything. Note-all these colors were not available in my Reeve set. One definitely needs a palette and a mixing area. The paints can be covered between uses and can be misted to use them later.
I have heard several people recommend Cheap Joes and Daniel Smith as good places to buy art supplies online.
Another fun site to check out is
Susie Short She offers several Watercolor Techniques free and sells beginning supplies too.