1. No, they are below you. You are still on the stairwell. You can see them through the grating floor, but don't have a clear shot.
2. The pair of droids are only covering the lower stairwell. Depending on how you get off the stairwell, they shouldn't see you taking out the snipers.
3. There's debris and machinery in the way, but it's possible to get the escape vehicles to overrun two of the trooper positions. The other two are behind structural supports, and the techs are in the back corner.