I saw your finished painting, it was quite nice. I recommend understanding tones and values before working with color. That would allow you to focus more on the light source, giving your painting a form and structure. Using photographs as reference is fine, but it's not very effective unless you have a general understanding of what you draw already. Using photographs as reference can make your paintings turn out flat. Just in everyday life, observe how certain body parts or things move.
When starting out, you should just be using a hard edged brush, and a soft edged brush. Don't concern yourself with other brushes so that you can practice how to actually paint things without using 'gimmicks'. You can paint with multiple layers, but I personally don't like layers, so I try to use only 1.
If you disregarded everything that has been written and want to start working with colors right away... then I recommend not blending with 4+ colors. If you do that then your colors tend to turn out muddy looking.
Once again be careful when using a photograph reference.. because you have to think if you're actually painting what you are actually seeing in the photograph. Are you drawing/painting optically? Or are you assuming that said color or line is meant to go there. I think it's more effective to find a digital painter that you admire, and look to see if that artist has already drawn what you need a reference for(hair,clothes,eyes,etc.), and try to retrace their steps. Hm... Lastly.. be aware when rendering. Don't over render things. Leaving some parts partially un-rendered gives your painting texture and looks more interesting as opposed to a completely smooth panting.