I'm glad you decided to post this. You should feel inspired and encouraged to practise and improve by artists like Shade, not give up, or feel unworthy! After all, they were beginners once and only became as good as they are today through practice, hard work and getting feedback.
I think your idea is a good one and that your choice of colours is good. You've got a pretty good idea about shading and tone but you just need to practise this area more, and try to get your texture smooth.
I hope you do another colouring soon! Why not check out our MH Academy for tips and advice?