long - at least 3mins, but I find 4 mins+ better
allows the neural system to recover - at 3mins, it is only partially recovered. The higher the rep count the longer the rest I find - like to remove all pump if I can help it.
As far as sets, its partly up to each person, the weight, the goal, the reps etc.
better to go lower than higher. You cna bukld up over time as your work capactity improves. Sometimes I go as low as 2x3 or 3x3 to as high as 10x3