As far as players go, it seems to me that NPCs and your physical player are the only things that have facial movements, and even move for that matter without being prompted by you. However, your player can't move his mouth (Question 1: Is there a way to change that?), walk without anything in his hands (question 2: Can that be changed?) or move his eyes (Question 3: Guess).
Basically, what is the best approach for having people in a Gmod machinima look natural (preferably that you can do by yourself).