Why is a bent ram's horn the most preferred choice for the Mitzvah? If one has available either a straight ram's horn, or the bent horn of another species, which is preferred?

What is the minimum valid size for a Shofar, and why? Is this specification of Biblical or Rabbinic origin?

May the horn of a non-Kosher animal be used for the Mitzvah?

If the Shofar developed a crack or puncture, is it still valid? What conditions are necessary for filling in such a crack? Is plugging the hole with one's finger sufficient?

For what reason does one not fulfill the Mitzvah, in a case when his act of blowing of the Shofar involves the transgression of a prohibition? Is this a standard example of a "Mitzva ha'Ba'ah ba'Aveirah"?