I disagree with the first statement because, I think students love to sing but we have to choice the appropriate songs depending on the age of your students.
In the second statement I agree but sometimes is good to change the routines of your classes so they can change the way to work and we can plan an interesting activity.
finally in the last statement I think student who finish quickly can help other classmate with their work and of course
we can give extra work for them so they can review the topic.