50 grams should be more than enough. In fact I think some folks around here use less for anxiolytic purposes. If you haven't tried boroguru before I would do a test run *before* this day in case you get nauseous or something.
Unusually stressful events are not the best times for experimenting with kava... but that's just my opinion. Talk to your doctor/therapist/counselor beforehand, try to find a couple different strategies for dealing with stress.