Brushes come in various materials, sizes and shapes. You don't need many, but each should be chosen with a definite purpose in mind.
The following video, describes a small useful selection as well as their uses.
Large Round Brush (No 12, Natural Hair) ... I would probably stick with a #6 and a #10
How many colours do you need when starting watercolour... and which ones?
Paint manufacturers - like Daniel Smith - offer over 200 different colours; but students can do quite well with 6-8 well-chosen ones; and even professionals do most of their work with only a dozen.
The reason is that any colour can be obtained by judicious mixing. Theoretically, all you need are the 3 primary colours: Red, Yellow and Blue. By mixing any two of those primaries in various proportions, you can obtain all the colours in between - as shown on the Colour Wheel. For example, mixing Yellow and Blue gives you various Greens, Red and Blue gives Violet(s) and so forth.
Lighter versions of a given colour are obtained by using more water and less paint. And you can darken a colour by adding its complementary - the colour opposite on the Color Wheel. For example, to darken Red, add some Green; to darken Blue, add some Orange, etc... and a perfectly balanced mixture of a colour and its complementary can give you Black.
Unfortunately, every pigment added to a mix reduces its intensity. So, in order to simplify mixing and obtain bright colours, a practical palette usually includes pure (single pigment) complementaries in addition to the primaries.
More elaborate palettes will select colours distributed evenly around the colour wheel as well a few personal favourites.
Any choice starts with the 3 primaries to which we add some useful secondaries - not necessarily all three. A good example is
Dawn McLeod'sstarting palette of 5 colours which adds Green ( for landscapes ) and Burnt Sienna to use with Ultramarine. This gives:
Red: Permanent Rose (PV19)
Yellow: New Gamboge
Blue: Ultramarine Blue (PB29)
Green: Sap Green
Orange: Burnt Sienna (PBr7)
Note: Abbreviations like PB29 and PBr7 refer to standard industry pigments. See the HANDPRINT Site for more details. That site also gives an advanced colour wheel showing the exact position of each pigment.
Minimal palettes are useful for beginners who learn best with a limited number of choices. They are also popular with Urban Sketchers who must work quickly in crowded environments.
The next step: Split Primaries
It is difficult to get a full range of bright mixed colours with only 3 primary colours.
Consequently, artists normally progress to a split primary system, which uses
2 versions of each primary colour - a cool (bluish) one and a warm (yellowish) one.
Typical is the split primary palette used by Kateri Ewing in her colour mixing course ($$) on Craftsy. Most are from Daniel Smith (DS) .
Cool Yellow: Hansa Yellow Light (PY3) or Lemon Yellow Warm Yellow: New Gamboge or Indian Yellow (Holbein)
Warm Red: Transparent Pyrrol Orange (PO71) Cool Red: Quinacridone Rose (PV19) or Permanent Rose
Warm Blue: French Ultramarine (PB29) Cool Blue: Phthalo Blue, Green Shade (PB 15:3)