I am not anti caffeine but most people get WAY too much caffeine. In moderation its fine but too much will raise cortisol levels and lead to adrenal fatigue.
Coffee has a lot of health benefits associated with it so you would be way better off drinking a cup of coffee instead of taking a caffeine pill
No it is not at all important. I limit my consumption of coffee to one cup of black coffee per day which I consume immediately prior to my daily training sessions - fair trade, shade-grown coffee, of course.
100mg preworkout is very mild in my case, works well and i barely feel it. Also notice the large amount of teens who are skinny fat, oily and have bad acne from drinking monsters everyday.