1. Because there are ways to resist the veritas serum
2. Because he needs to be in Hogwarts to do that.
Also that curse wasn't that powerful it just prevented someone from doing the Defense Against the Dark Arts job for more than one year.
There is not a special Auror job that he could curse and also there is no reason for him to do that.
3.That has nothing to do with the love potion but more with his parents.
4.Because of Time Paradoxes. A girl that visits more than one class room during the same time is not a threat. Also there is max time you can travel back in time (around one hour or so).
5.How should he know about the Marauder's Map? Because children bully each other that is something that happens and you should not always get involved in such things as a teacher. (except if it becomes too extreme)
6. Because Hogwarts has spells in place that will protect the students from accidentally murdering each other.
7. Because the age at when you are considered an adult is chosen arbitrarily by all countries. Humans are biologically mature when they can create offspring aka 12-14
9. There is history and other things
10.Because it is ollivanders company secret.
11.Because they receive honor
12.Then voldemort would have gotten the secret very easily.
13. Because the Dementor's kiss is capital punishment.