Hi, in an application of mine i use the Qt Mobility Camera API.
Most of the camera operations are taken from the project: https://projects.developer.nokia.com/qcamera/ which is pretty good to get a quick handle of it.
Further more i added a simple function to toggle the flash which looks something like the following. It is completely written in Qt so i thing you will find what you want
QCameraExposure* cameraexpo = m_camera->exposure();
This answers to your first question. Regarding your second question you can try playing with the different flash modes.