Its ranked in the order of effect. No carbs/sugar and instead eating only veggies and grass fed beef/fish is very noticeable to me. I am absolutely my better self when I am on a keto diet.
Yes, and to me good sleep is highly correlated to physical and mental health and all what is mentioned affects one or both of them.
Is not a matter of just to wanting to have good sleep but try to solve other problems such as food, alcohol, cigarettes, drugs, lack of sport, caffeine, …
It's possible that #3, good sleep, is the most important element, and adopting the remaining behaviors largely work because they improve sleep quality.
Drugs or alcohol can reduce sleep quality (e.g. cannabis reduces REM sleep, alcohol can cause you to wake up too early); a diet high in simple sugars can negatively affect sleep quality [0]; and porn at night can mean looking at a screen with blue light, which can cause you to fall asleep later [1].