Creating eyes

I am a beginner with Toon Boom, I am dowloading the tutorial videos, but I am trying sth by myself but I am not sure if I am doing well, let’s suppose the following for an eye like the little einsteins:

1.- the exterior of the eye (white area)
2.- the pupil (brown)
3.- the reflect
4.- the black hole (black)

A.- Is there an easy way that if the 2nd layer is out of the 1st it is not visible?
B.- 2,3,4 is better to have in separate layers or in the same, Can I always move them inside the same layer?

Thank you, I want to make my first well done animation.

usually we create an eye as one layer(drawing). In cut out style, left and right eye are separated into different drawings. Put all the part of the eye that you want to animate into one group of drawing. Then, you make a copy of the eye then paste it in a different level of the same drawing(first eye in no 1 then the second one is the next number and so on), change the position as you like. Just like creating key animation.
When you want to animate the eye, use the slider of the drawings property in the right panels.

In short you design every possible movement.
hope this helps & clear enough