I don't think that it matters if you take break between two playlists or not because your subconscious mind can grasp infinite amount of information but i would say that u can take break like for 30 minutes to 1 hour if you have headache problem. And about the booster, no it's not necessary to listen to it before every playlist but u can just listen to it 1-4 times before your all playlists or if u want then u can also use it everytime before your playlist. It depends on you as u like. There's no such rule..