1. If your goal is to actually build something you will be infinitely better off starting small and simple and working from there. Divide your project into smaller sub projects, such as a finger then a hand, then an arm, then a head or leg joint and it will be more satisfying and less expensive. Plus the trial and error you go through making one joint work can be applied as your joints get bigger, more powerful and expensive. Since humans are symmetric you can also apply your successful designs to the other side of the body.
2. skin is kind of jumping the gun but castable silicone or urethane like that used for masks would be easiest to use. I have a friend who uses it in art and it looks straight forward.
3. Unless you have very deep pockets, you would be better off designing from the inside out not the outside in. In other words, start with stock items for joints such as servos, gear motors and brackets and design out from there, as opposed to starting with the finished exterior dimensions and then trying to fit everything inside.
