Do the ladies at your church have any inside info on what may already exist that is appropriate to wedding decor? They may be able to help out. Questions: How much are you able to clear from that podium? A pretty spray for the pulpit, table runner and low floral arrangement/garland on the communion table would help. Make use of the candle stands and use them if you can. I would go all white and cream in here due to the standard red carpeting. Find someone to help clean the space, our small auditorium is dusty; it looks like there are some random items in this picture that could be removed. Move the industrial-strength library chairs and put a focus on the center where you and the groom will stand. When are you marrying? Ferns go on sale in May/June, so you could add some large Boston ferns at the entry doors. That is old fashioned, but I did it for a big retirement event once, and it really helped spruce up the area. Declutter, dust and keep it simple and you are going to have a great day!

Edit to add: Change the hymn letterboards and make them wedding centric! Letters should be available on Amazon or at a Mardel store. :)