Some additional comments:
2) Yes, the ability would count. You could even win the battle, when all your units are destroyed but a siege tower activated its ability before. Stated in the Rulings FAQ at http://boardgamegeek.com/filepage/52411/various-rulings-from...
3) No, you can't. Even if you would choose the same unit for both activations the unit would still be routed and not routed and then killed (what probably is the reason for the question). The ability says: The Units are now routed (if already routed they will be destroyed). You don't rout them and check again. Only rout them (or destroy them).
4) Yes that would be 4 damage, as you can choose the one giant. And @Dweeb. You can have multiple damaged giants, e.g. when they fight against a hellhound and it triggers its special ability.
2) Yes, the ability would count. You could even win the battle, when all your units are destroyed but a siege tower activated its ability before. Stated in the Rulings FAQ at http://boardgamegeek.com/filepage/52411/various-rulings-from...
3) No, you can't. Even if you would choose the same unit for both activations the unit would still be routed and not routed and then killed (what probably is the reason for the question). The ability says: The Units are now routed (if already routed they will be destroyed). You don't rout them and check again. Only rout them (or destroy them).
4) Yes that would be 4 damage, as you can choose the one giant. And @Dweeb. You can have multiple damaged giants, e.g. when they fight against a hellhound and it triggers its special ability.