My rov in Yerushalayim who is a member of the Badatz of the Edah (for those who wonder – yes, I am different now from how I was in the past) told me this:
* Even half a cup of grape juice is enough.
* There is no need at all to sleep.
I myself have never been drunk and intend to keep it that way. The only thing I use on Purim, as well as for Pesach and every other shabbos/yom tov, is grape juice.