I’m in the same boat, and inaccurate as it may be, I’ve been looking at pictures and attempting to count the stems. You probably aren’t ordering from Sam’s with those types of flowers, but if you’re interested, they have a mixed flower filler that has statice, queen anne’s lace and some other stuff that would probably look really nice with the flowers you’re using.
From what I can tell, most bridesmaids have 20-40 stems, brides are usually start around 30/35 to 60+ for a big cascading bouquet. Corsages are usually 3, Bouts 1, both plus filler. Flowergirls seem to have 8-12 depending on the style and size of girl, more if you do a pomander though.
Centerpieces seem to be more like bridal bouquet range, unless they are either very short or very tall (perhaps with branches). I had wanted full, domed bouquets, but went for tall to save $$ (and time arranging/preping). Figure anywhere between 12 to 60+ for centerpieces. I looked at oodles of pics to find a centerpiece with not a lot of flowers in it that I liked, and was able to find a few, and they tended to be tall so you get a lot of impact from a few flowers.
This puts me at about 425 flowers for me, toss, 3 bridesmaids, 6 corsages, 10 bouts, 2 flower girls and 17 centerpieces. When I was looking at shorter but more full, domed centerpieces, I was at about 730 flowers, so going up rather than out is a huge savings. I figured this out by making a spreadsheet with all the people/arrangements in one column and types of flowers across the top. I kept track of how many of each flower came in each bunch at the top of each column, and in the end row had the target for number of flowers I wanted in that person’s arrangment (so for my row, column 1 said bride, column 2 was x roses, column 3 y delphinium, column 4 z filler, column 5 total of x+y+z, and then column 6 to remind me of what I was aiming for (in this case 45-55)). This seemed to work pretty well.
I’ll be using delphiniums and bells of ireland for height and wasn’t initially sold on them, but when I did the math, I decided it was a great option since we’re using blue anyway and they are cheap and take up lots of space in a verticle arrangment like this: