You could certainly add a lot more blooms to this particular design. Consider large mass flowers like hydrangeas and allium.
The most important consideration is the delivery (which is why you see florists with rather large delivery vans on the road.)
Since this does flower up quickly, you could just take the greened spray to the church, transporting the flowers in a bucket and then flower in the spray quickly upon arrival.
I always finish my wedding flowers by giving them a good misting of Finishing Touch. This is a flower sealant that keeps the petals hydrated and slows down the transparency of the petals.
I always take it with me when servicing a wedding and give all flowers (including the bridal bouquet, corsages and boutonnieres) a good misting then allow to dry before handing it off to the bridal party.
I have many more step by step flower tutorials, including ones for bridal bouquets, boutonnieres, corsages, church decorations and reception centerpieces! Check it out.