As artists we spend a lot of time mixing colors to get just the right look to evoke mood, realism, style, etc. However, a lot of artists get hung up on the right tube of color without understanding the concept of mixing the color one needs. Is it better to have hundreds of tubes of colors so that one can have the color they need? The simple and quick answer is no. Throughout history artists have been on a quest to develop a simple yet complete palette of colors to suit their needs. Why? Because it is always to better to be a master of a few colors than a blind user of "too many".
So how much is "too many"? It really depends on you and what you are comfortable with. I like 13 colors (includes black and white) for studio use and about 7 when I am working en plein air. With that said, I focus on versions of the primaries (red, yellow, and blue). I don't purchase greens because I have always liked my mixed greens better than anything I have ever tried from a tube.
If you are struggling with your colors, and you are overwhelmed with mixing, find a handful of your favorite primary colors and start mixing for practice. Use white to lighten the mix but be careful using black to darken. When darkening a value of a mixed color try mixing a dark color version first using a darker primary and see what happens when you add white. You may end up with a few more darker values of the color you mixed and have good light value versions to use too. For example, if lemon yellow and cadmium blue make a nice green but it is not dark enough to start with, try using cadmium yellow. Play with your colors and make notes.