1. The structure and the wet-weather plan B
This is item number one. Even with fine weather forecast, a reception tent is the insurance for your wedding: it shelters your guests from the sun, the wind and an unexpected shower.
Choose a structure sized for your seated dinner (1.4 m² per person minimum) with closable walls that can be lowered quickly in case of rain or wind. Also plan for a covered area for the drinks reception and a sheltered route between the zones.
The plan B is not an option: it is the heart of the setup. A tent with walls ready to close turns fickle weather into a non-event.