There isn't one! Wear whatever makes you comfortable! (But maybe dress for the weather, as the barn has only so much climate control.)
No. Due to the property agreement and for everyone's safety, no persons are permitted in the water - please let your children know and keep them clear!
Whatever color they want! Which means you also can wear whatever color you want, no one will care if you end up matching!
There will be a limited amount of beverages provided. Further beverages will have to be purchased by guests. The couple lovingly asks everyone to keep their celebration to a tolerable level of stupid.