Fixed Portrait Shoot

ISO 800 

aperture: 7.1 shutter speed: 1/640

ISO 3200

aperture:1/1000 shutter speed: 13

ISO 1600

aperture: 1/640 shutter speed: 13

ISO 400

aperture: 5.0 shutter speed: 1/640

ISO 100 

aperture: 3.5 shutter speed: 1/640

1.  I think 1600.

2.  3200
3.  Yes
4.  I learned to keep changing the ISO and everything so i can get a better picture.