I think that using a tablet for smaller resolution pieces is a matter of preference, though I do believe that an optical mouse requires less dedication to enjoy. Unless you have a very large tablet- the controls will not be as pixel perfect as an optical mouse's would be, and it would take some amount of effort to compensate for that. Furthermore, if the mouse buttons are used in any way during drawing that is just one more task that takes getting used to. I find that the buttons on the pen are in an incovenient place in comparison to how I hold a pencil or pen. I'm apt to believe that I am not the one exception.
As for your avatar, coran, I believe you should study some images of human eyes in order to get a grasp on how they look. Also, per Adam's suggestion, shrink down the size and work in a few gray tones. This will help you better appreciate the conciseness of pixel art, while understanding the importance of shapes, contrast, and lighting.