1: Until you've memorized the tracks completely, it isn't good to just hold down the speed button all of the time. For the turns, unless you're going for a REALLY good time, it's good to go at normal speed, and focus on not hitting a wall, because that's mainly what can cost a lot of time.

2: You can pause, and hold the speed button to speed up without jumping.

3: You can hold both of the buttons to shift the map in a direction to shift it at twice the speed.