Hi there :) Your art is quite lovely and I'd say you are quite talented. I'm an artist myself, by freelance work, and I work with photoshop - though to be honest, all programs are good, it depends on which one you -know- how the artwork turns out in it. Keep it up !
Also if you have a lot of trouble with trying to see where the shade sits, the best thing is take a photo and look where the shade is falling, its one of the very first exersizes in advanced art classes - the imitation of what happens in real life. Your eye will eventually learn to recognize areas that should have shadow in them :)
But to be honest, yours is very nice!