variable pitchP :
The second aircraft should only be cleared as the controller sees the first get airborne, this is pretty basic is think
Yes in Europe but not in the US where the 6000 ft rule applies ( you can clear an a/c to take off provided the preceding has passed the 6000 ft mark)
Most of the Canadian ATC rules are based on US ones , although I am not sure in this particular case it they are exactly the same .Someone from Canada can confirm or infirm that.