Find out about the lighting situations (venues, etc). Then plan around that.
Then practice doing your candid shots and semi posed shots.
What I would do if I were you is do an 'engagement' or pre session with the couple. That way you get your practice and they get to see what it will be like with you. If you end up liking the results (with all parties involved) then great! If you guys don't, then time for plan B.
I think you should have an assistant and or second shooter. Her other cousin can be the second shooter. You should have an assistant. I wouldn't personally have your assistant carry a remote wireless flash around unless you work with someone and you have a seemless way of working together.
Depending on your style, I would use fill flash for outdoors and bounce flash for indoors. For group shots, probably that would be the only time I would use lights on stands to ensure everyone gets even lighting. You want to be mobile so practice fill flash (perhaps with an L bracket?) and bounce.
Prepare with your shoot plan/schedule prior to the wedding. Have it all in your head. But then let it all go on the day of the wedding and go with the flow. Just be there and go within the moment. You'll be a fly on the way and be that 'editorial' or 'photojournalist' recording a very important event.
I think that's about the only and best advice I can give. Hope it helps.