I was recently looking about for wedding guest dress and/ or some springy-guesty tops to work with some bottoms I already had ( a burgundy skirt and some black wide cropped pants. I had tried some things online and then wandered about in a large department store.
I had no luck and will likely wear something I already have ( there’s no place like home!) but it was painfully fun to try things on and re- learn things about my style preferences. And be reminded that dresses are hard for me! I do better with separates but have trouble getting all the right pieces assembled.
Anyway, one constraint I have is shoes- I have actually 4-5 pairs of ankle strap shoes that will dress outfits up a bit, black , navy, burgundy, 1 is bronze, 3 flats and 2 with small heel. Right now, anything I wear for “ dressy” needs to go with one of those.
So, you might also think about building your outfits from shoes up-/ either if the venue has rustic footing, or if your feet are fussy.
If you are the lucky type who can wear many toes of dressy shoes or easily find new shoes to match dresses, then it may be easier.