You need a place like a church, a reception area near the church, a party location afterwards.

You need someone to do the ceremony and someone to do the party, maybe including DJing and doing the fireworks.

People always want some awesome cake and most probably some photos taken, too.

So mostly the same as rl. Just more lag.

you need awesome food and an open bar.

Goes without saying ... only way to get through a wedding even in SL - booze, booze and more booze