When I got married, in July about a mile from the lake, my dad had the outdoor area "bug-bombed" the day BEFORE the wedding -- or maybe it was 2 days? Whatever. But it seemed to work.

I don't know about citronella candles, but I learned here on this forum that the best defense is a FAN. Hard to have enough of those for a big area, though, and I don't know if you will have electricity.

Thing Two (my daughter) worked at a camp this summer, and she used one of those new things you clip on your belt -- I think it is a fan with some insect repellent? She said it worked great. You could consider buying those for people.

We burn the "Off" mosquito coil incense rings. They work very well and don't smell bad.
We also spray the perimeters of our yard with the kind of mosquito repellant that comes in a spray bottle with a hose attachment. It is safe for kids and animals, and doesn't do any damage to my plants. It is great for gardens where the little varmints like to hide in the shade of the plant leaves!!

Here is a link that might be useful: live link

I'd like to emphasize that you should not spray the whole location with pesticides. They can be a toxic overload for many people: the elderly, the very young, pregnant, anyone taking medications that are hard on the liver (just about everything), anyone recovering from an illness, and anyone with acute chemical sensitivities.

Big fans work well, as mentioned earlier. Your event planner could locate some nice ones on tall pedestals. Mosquitoes and gnats are one of the reasons why we have big ceiling fans on our porches, here in the South.