I am going to try some annuals from seed this year. I live in Spartanburg, SC (hot) and have to worry about deer. So...sweet alyssum, four o'clocks, marigolds, and zinnias are on my list. I will also plant some sweet william but, as I understand, it will not flower in spring/summer. But I will take the greenery and hopefully it will spread nicely. I have a rather large rock garden that needs some hearty flowers/ground covers. I bought bunches of seed from WalMart and Lowes and bunches of bags of top soil. My compost is ready too. Gonna plant soon after March 20 (early spring) for some and a bit later for others. Here's hoping.

skhaire, 'big back yard' is awfully vague. How big is the planting area? Does it have a regular water source? Is there any pitch and roll or is it flat? Are areas shaded or is everything in full sun? How much time do you have daily to fuss with weed pulling and do you know what's a weed and what's a baby 'wildflower'?
Those purty photos on those big bags of mixed seed make the task look as simple as the bigbox commercial where the gal hauls out a carpet and flings it on a 20'x20' area for instant flowers,shrubs etc...color.
Not gonna happen. Those plants that do rise and take might have a spindly bloom that lasts maybe two weeks and after, you have a scrawny plant with no color most of the season.

Measure, take note of sunpath/shade protection from 2PM on to sundown, soil preparation, prevailing wind and how you plan to keep the area appropriately watered.
Gardening is not simple..if it were, nobody would have lawns.

LKZZ..good choices although the alyssum might suffer in the heat some.If you shear it after early spring bloom, it should re-flower in the fall. The standard white makes a nice edging and the honeybees love it.
I have deer also in each of my yards and one flower that they leave alone is 'million bells' calbrachoa. It also has returned reliably for 8 years now in a raised natural bed which gets regular irrigation. It comes in all sorts of colors and looks like a small flowered petunia.
Geraniums of the species types (even the hothouse ones) are not bothered by deer and arctotis (iceplant) is reliable in hot dry areas with occasional deep watering. It does close its fuchsia colored flowers in late afternoon so it makes a great underplant for your marigolds and zinnias.
Since the iceplant is a perennial (and pieces root in water easily to spread to other areas), suggest you bury a couple of goodsized plastic plant pots within the iceplant bed so when you plant your annuals you don't disturb the perennial roots. At least a quart or a shallow gallon pot should give most annuals enough anchorage to withstand
normal winds.
I've done this with goldenlime green coleus among the fuschia colored ice plant and it is a visual pop 50' from the street.