Cute art, and super good for your first attempt at digital art! 'w')b
Hopefully I'm not overstepping too much, but a bit of advice for shading that I quickly scribbled together
(because when I first did digital art, I did the same thing until someone told me similar things):
I tried to keep it simple to things you're probably familiar with already -- you'll learn more as you experiment more 'w')b (e.g. painting, finding other brushes you like more, etc.)
For the colour-picking part, you can actually choose from a bunch of different colours, it just depends what you like best and what you're comfortable with!