Hey 52niner, looks like you have most of those questions explained. So i'll just answer the last one :)  For the APU you always want to have it turned off before takeoff.  Most 757s turn the APU off as they start their taxi to the runway.  I'm sure you have noticed but there is an APU door at the base of the tail thats open when on.  Wouldn't think it would be a good thing to have this door open any time during flight.

Travis