Shofar Blowing – When Have We Fulfilled the Mitzvah?

What should the shevarim and teruah sound like? What are the different minhagim?
The tekiah’s tone changed or wavered in the middle – is it still valid?
When is it necessary to repeat only that particular blast, and when must the entire set be repeated?
Is there a reason to hear more than 100 blasts in order to fulfill the various minhagim?