A 12" ws should work depending on the wing area so you might
want to fatten it up a bit. Yes a smaller plane is lighter but may
not hold up the weight of the AA guts in flight. You might want
to build a stick wing and instead of tissue use Reynolds plastic
wrap. It's a bit lighter.
I still don't believe you could slow the plane down enough for a
living room flyer. Would make a great gymnasium flyer though.

Also the motors on your previous plans are too close together and
the angle of the wing should be moved a bit higher on the leading
edge. There should be some upward thrust from the motors to the
wing to help give it lift.