Jena, think about springing for some shrubs and perennials as well, as some bigger pieces will make it look more like garden and less like a bouquet. The other side of that is when the wedding is over and then winter rolls around, followed by spring, you have some bang of your buck still, as shrubs and perennials add to your garden for years to come... annuals are certainly a good way to go to add color, but don't forget to add some form as well...
[url=https://www.whiteflowerfarm.com/26630-product.html]Clematis paniculata[/url] would be great, covered with white, fragrant flowers. [url=https://www.finegardening.com/plantguide/clematis-tangutica-golden-tiara-russian-virgins-bower.aspx]C. tangutica[/url] would be another good choice; even if it has started to go to seed the seed heads are as good a show as the flowers, sort of silvery and delicate. It's common name is Russian virgin's bower, but I guess you'd have to check with the bride and groom to see if that's apropos...

Nice call RG!
HG