QWhen playing this follower's automatic ability, if I can't select an enemy follower on the field, can I still choose option 1 to have nothing happen?

ANo. If you can't select an enemy follower, you would be required to choose option 2.

QIf I evolve an Eidolon of Madness on my field, does this follower's "whenever a follower on your field evolves" ability trigger?

AYes, it does.