1. RTH Offset can be set in the Settings. If your flight altitude is 100 meters and your offset is set to 0m it would fly home at 100 meters. If it is set to 20m it would come home at 120m. When using Terrain Awareness it would come home at 40m on top of whatever the highest terrain encountered on the programmed flight path would be. This is only valid during uncontrolled RTH events that are triggered by the remote, battery or aircraft. If the entire flight occurs without being interrupted by any of these the return leg will be done at the programmed flight height.
2. The speed selector in the Options menu is the highest speed you want to allow during any part of the flight. This will be what it flies on the approach and return legs. The maximum speed on the mapping flight path is determined by the camera parameters and layout geometry. On the mapping flight path it will be the set value or slower.
3. Nope. We did that once and everyone flew into trees.
4. We hear that a lot. We will look at that. This is something that could be set in the Settings.