Well, the stress levels are beginning to rise

A couple of friends asked me if I would photograph their wedding. I have done quite a few for friends ( I should know better) and fortunately went well in the past. This time The hotel are allowing us to set up studio lighting with a background. The guests are arriving at 11am although the ceremony starts at 12:30.
Our aim is to photograph as many guests are willing before the ceremony begins. My wife (who seems to thrive on stress!!) will be taking these while I saunter off to photograph the bride at home.
I have done the usual checks. All equipment, backup equipment, spare body checked. All cards (15GB worth) formatted, Lenses cleaned etc. Batteries charged. Cameras set to ISO 100 (to start) and WB set to auto until i can do a custom. Have I forgotten anything?
The Bride has hired a horse and carriage. The question is, and I know I've left it late, any tips on getting the best composition regarding the bride and her transport?
I have a few ideas but would welcome some input.
By the way, I am to be a grandad for the first time

Many thanks,
Martin