I've seen it suggested that V can leave a possessed body (becoming a disembodied spirit) but not his own. I don't recall seeing anything (either in canon or in HPMOR) that confirms or refutes that.

I share your concerns about #2, although generally "once you have physical access to the hardware, it's over" -- if you can catch Voldemort or Dumbledore or whoever asleep, you can smash their head with a big rock or something.