I'm waaay to tired to remember her requirements exactly so I won't post in case I'm just plain wrong.
Turn 2 is the soonest you can bring an Avatar out. And when you do bring out your Avatar it counts as summoned HOWEVER they don't get slow. The avatar gets any leftover General AP and can use any of it's free action abilities, for instance Avatar Zoraida has Casting Expert so she can avatar up and pins and needles twice.
One rule I'm not 100% about is whether or not a master using something like Fast (lilith) then going Avatar, if her Avatar can still use Fast. Pretty sure the answer is no. The Avatars work very similar to how Chompy and the Dreamer work, except it's a one way street. Once the Avatar is out, it's out for good.