I used to grow flowers for dried arrangements and wreaths, as well as pick wild ones. I had uneven success. One of the best perennials to grow is lavender (many uses) . I did all right with globe amaranth but not the other kind. Sea holly was hopeless, but bells of Ireland did fine. Strawflowers were pretty reliable, as was sweet William. Of the wild ones, I liked yarrow (for its scent) and pussytoes (because it looked pretty in small dainty wreaths) best. Sweet pea is easy to work with and looks good for a while, but fades over time. The one to start with, I think, is baby's breath - I found it abundant, trouble free and attractive in any combination.
For large arrangements, I liked to cut young bullrushes and Alexanders and hang them upside down in my semi-dark storage room until the goldenrod (including galls), the teasel, globe thistle, and Pampas grass were ready.