Wow, your house sounds cool!

Knock-Outs stay green here in 8a, but not the salvias;
salvias may be evergreen in your 8b zone, & of course the bearded irises are evergreen, & the muhly grass, while not evergreen, does retain its foliage through the winder.

Salvia greggii is blooming here already, & the early/mid-season irises are just beginning.
the salvias will bloom thru summer.

As the year wears on, ruellia (Mexican petunia) will bloom & will continue until cold weather, as will zinnias & probably your coneflowers & daylilies.

Someone will undoubtedly know more about the other flowers you mentioned.

Here, I like coreopsis in the summer, but I haven't figured it out yet.
It seems to go full blast through the heat until one day it...croaks.
This summer I'm going to trim it after the first set of blooms start to fade.

Crinums are big, splashy, showy flowers & plants;
if you go to the San Antonio swap, Tally often has crinums to share.
Crinum dies back in the winter, but I think it's worth the space it occupies!

If you have room, flowering trees are wonderful.
redbuds are the first ones to bloom, in spring, followed by vitex/chaste tree, & then the crepe myrtles go wacko all summer.

Late summer/early fall, obedient plant, lycoria radiata, then goldenrod (which looks good with the tall Mexican petunias).

I'd say mix the annuals with the perennials;
only you & the plants will know which is which anyway, & you can have a much broader pallette that way.

You might use annuals that are self-seeding, so that you don't have to start over every year.
Zinnias, celosia, ornamental peppers, & morning glories are annuals that return year after year.

On your fence, you might use coral honeysuckle.
It's a beautiful coral color, & it will eventually cover the fence, & it's evergreen.

Best luck, & have fun!

edited to add:

How could I have forgotten Lady Banks roses???
The bushes are so large that people here use them for shrubs, but if you have the space they're enchanting.
Pale buttercream button-sized little roses cover the bushes in the spring, & after they fade, you still have a *thornless* evergreen shrub.

It's like once an Iris is done after blooming for 2 weeks, is that it??

It is for our old/heirloom pass-along irises. There are newer reblooming cultivars that might be worth a look.

Some other good long blooming candidates include 'John Fanick' or 'Victoria' summer phlox, Russian sage, gaura ('snow fountain' is a nice one), Mexican hat, Turk's cap, zexmenia/orange wedelia, and Texas lantana (l. horrida).

Other lantanas (l. camara/l. montevindensis), esperanza (tecoma stans), blackfoot daisy, and four-nerve daisy are also very nice, but do not always return for us in the wet freezing Dallas clay - most are still worth it even in the years/locations they only work as annuals.

Agree with silviatexas2 on coral honeysuckle (lonicera sempervirens) for the fence. Cultivars are available in several colors. Flush of flowers in spring with some intermittent blooms into the fall. I like it because it is tough, but stays in place. Crossvine is another good well-mannered native evergreen vine that is currently putting on quite a show. Natural colors are orange/yellow, but believe there is at least one red-ish cultivar ('Atrosanguinea'?).

Plants near the foundation can also be evergreen bushes or shrubs, not just perennial flowering types. However, even those shrubs can provide a great array of flowers at the appropriate time, or be the live trellis upon which an annual or perennial climber uses.