Is it permissible for me to remain in my current job, with a Christian woman supervising me, for the purpose of removing her from the company, and will I be rewarded for that? And can I become an Imam for Muslims while a woman works in my department?

Mixing between men and women in work and study is forbidden, and men are enjoined to work and provide for their families. It cannot be said that righteous men must leave their jobs, as this could lead to greater harms. It is permissible to remain in a mixed-gender work environment if the anticipated benefits are real and evident, and the employee is able to control himself and avoid privacy with women, and does not find inclination towards women in his heart. However, if the benefits are not evident, or if there is weakness and fear of being affected, then avoidance is preferable. There is no harm in taking on the imamate, and perhaps Allah will benefit the people of the area through it.