1) How are Islam and Christianity so similar, yet so different?
What separates the two is that Muslims do not believe Jesus was the son of God, they believe just like Christians that Jesus was the messiah, but not the son of God. The Quran and Bible have many similar stories. Islam's traditions have not gone through a transformation like Christian traditions.
2) Does Islam encourage violence?
Not necessarily, it's the interpetation of the scriptures, not the scriptures themselves. Islam is a religion of peace. The Quran says to kill infidels because later in life Mohammed had to become a warrior, but the infidels were specific to the time and have been dead a long time. The second part of the Quran does not supersede the first part. Often, modern, radical books have been quoted instead of the Quran leading to dangerous misconceptions. Politics poison everything, not the religion. Religion is used as an excuse for violence.
3) Does Islam oppress women?
Women in a free country feel empowered by covering themselves, but in other, much stricter countries, women are being oppressed. Sharia Law suppresses women by forces them to submit themselves completely to their husbands and other men. The oppression is more of a cultural thing, but countries with the largest inequalities between men and women are mostly Islamic. The Quran says men and women are equal, the culture changes the treatment of women.
4) Why don't we hear more about mainstream Muslims?
Muslims are afraid to speak out due to persecution just because they are Muslim. Feel like they need to be careful with what they say. People only hear about the radical Muslims, not the peaceful ones. The Muslims do not have a leader to help them speak out and show everyone that mainstream Muslims are Americans too and are not a threat.