I like 24/0. I also read that cannabis will grow 33% with 24/0 over 18/6. The main difference between 18/6 and 24/0 is just preference.

You put bags over clones to raise the humidity. It helps them get moisture out until the roots get established. I never see the need for humidity domes after a week to week and a half for some. After the domes just mist lightly.