This is my typical palette if you also include Titanium White.
I like the limited palette because it makes life easy. The simple questions become: lighter? darker? warmer? cooler? Not - Which blue, which red or which yellow? It just works for me. I can imagine that my palette will grow with my ability, but perhaps not. I like the simple approach. (Colors include naples yellow, cad yellow light, yellow ochre, orange, cad red light, cad red deep, venetian red, cobalt blue, ultramarine blue).
I always mix my greens.
Sometimes I use a medium of 1 part Stand Oil/4 parts Terps. If I want 'extra juicy' paint (as in highlights), I will use Gamblin Galkyd gel as a medium.
I also always brush or wipe my canvas down with linseed oil before starting to apply any paint.