Question about that: Will you only be able to roam around at just night or are you also able to interact in human form as well? Lastly, if it's RPed good enough will the AMPC be able to become a more permanent character to at least be extended? I know they start at level 10 immediately, so it probably isn't possible. Just wondering what the options really are.
Generally, AMPCs start at level 10 - ECL/2, albeit with good enough story and sound reasoning, some exceptions have been be made.
You are free to use the AMPC as you would a normal PC, aside of being a monster, of course.
AMPCs wont be made into permanent PCs, though. Their story arcs are supposed to have a specific beginning and a specific ending, spanning within a relatively short time, which is why they are allowed to start at that higher level.