Cathy
it is totally possible. I have bunch of small bulbs planted for spring show- muscari, chinodoxa, galanthus, eranthis hyemalis, etc- look up at Van Engelen site for more ideas. Then I have early blooming plants for my shady garden- pulmonarias, brunneras, columbines, bergenias. I am trying to have my beds made that way - every day there is something that is blooming and holding the show. For fall I would recommend anemones, asters, lobelias, late blooming geraniums as wlassovianum and yoshinoi, aconitums, trycyrtis, some lilies will bloom into August- early Sep. Lots of warm season ornamental grasses will come into its own during fall. Many sedums will have excellent show during fall time.
Many shrubs while not in bloom will provide excellent points of interests- many viburnums will give you leaf coloring and berries, hydrangeas specially quercifolia have nice leaf coloring change. My new spirea "yellow mellow" is colored bright orange- and absolutely stunning in the fall.
Not only you can put several seasons of interest in one bed but you can also plant them very close to each other- such example in my garden are columbines interplanted with anemones- I cut off columbines leaves when they done and anemones pick up the show, or early primulas planted under hostas.

Mums do good here in the fall and come back each year. It is possible to plan a flower garden with something blooming all time.
I would suggest writing your plan on paper. Use google to get information on plants and when they bloom.
When I first started, a single red tulip and white patch of alyssum made my garden look great in early spring. I have a christmas rose (helliborus) that blooms during the cold months of winter. After the tulips, the iris, lillies, and peonies bloom.
Right now I have tall phlox, marigolds, gladeolous, moon bush, 4 O'clocks, Impatients, hibiscus,sweet williams, petunias, geraniums, begonias, blue salvia, vincas and the cannas blooming, most of these including the zinnas bloom here up untill frost, also most of my roses. Don't forget the blooming vines. You might want to consider the knockout rose.
You can do it and have fun!

Thanks so much for your suggestions!
I'll be sure to check out the site, research and to write down a plan!
Thanks again!
Cathy

If you are looking for something similar to iris and daylillies, how about Crocosmia? In this zone they are just starting to bloom.