I'm slowly building a 4 season garden myself. So I wish you all the luck.
Unlike you all of my beds will not be in bloom all the time. That's a great idea. I find that managing to find plants that like the same type of soil, water, and sun and also bloom at different times is asking alittle more than I can do.
it looks like you are short the fall plants so I'll reproduce my list of those here.
Fall Blooming
flowers categorized by bloom colors available
The perennial grass miscanthus requires full sun and regular water.
The following are examples of colorful flowering plants:
Blue
flowers: monkshood, globe thistle, pale-blue flax, bottle gentian
Pink
flowers: Aster novae-angliae 'Alma Potschke' or 'Honeysong Pink', Japanese burnet (Sanguisorba obtusa), Sedum 'Vera Jameson',
roses, Aster, Suprise Lilies
Yellow
flowers: black-eyed Susans, dahlias, perennial sunflowers, ligularia, chrysanthemums, Patrinia scabiosaefolia, goldenrod, marguerite, golden asters
Purple
flowers: Joe-Pye
weed, asters, Russian sage, ground-hugging spiderwort, autumn crocus, Mexican Sage, Aster, Panzies
White
flowers: dahlias, chrysanthemums, sweet autumn clematis, Aster, Suprise Lilies
Warm Color Combinations: Helenium autumnale (red, yellow, orange, combinations)
Red: Pineapple Sage, Suprise Lilies
I am also working on some that bloom during the winter.
Adonis Amurensis
Erica Carnea "Vivellii
Erica Carnea "Winter Beauty"
Witch Hazel
For winter interest although they are not blooming at that time are the walking stick tree and the chinese lanterns. Note: the chinese laterns are invasive.
I'm sorry I couldn't give you a link. But this is what information I've gathered so far. I hope some of it helps.