I would avoid Maples due to the mess, diseases amd root structures. Dogwoods and Redbuds are understory trees so they prefer a bit of shade from bigger surrounding trees. Redbuds usually don't look nice in old age. River Birch will send up suckers as far out as the roots go. Cedars will make a mess on anything that is below them.

For inexpensive healthy plants, Santa Rosa Gardens has a good reputation for perennials, and you may get other recommendations on the perennials forum. Ask on the Hosta forum for recommendations for healthy virus-free suppliers of hosta that don't need to be the latest new plant. Regardless, before buying from any mail order nursery, check Garden Watchdog for reviews since often inexperienced gardeners (including me at an earlier point in my gardening hobby) order from nurseries that send poor quality or dying plants. On the left side of the linked page, type in the nursery's name to get their reviews. There is also a space where you can type in your zipcode or the zips of nearby towns to see what nurseries are in your area. In my neck of the woods, which is quite rural, there are a surprising number of nurseries if I want to drive a bit. Local plants will usually be larger due to the cost of mailing large plants, so I mail order unusual plants and ones that I can't find locally, and buy everything else locally. Often a short ornamental fence or a temporary fence can be used to train a dog to not use garden areas for play or toileting areas, though a vigilant eye may be needed when the fence comes down. I tend to use a wider mix of plants where I will be near the garden to enjoy it, but in a garden I only view from a distance, I am more likely to use massed plants for better effect. Both styles have uses.

I think this is going to turn out to be a learning experience for you over the next few years when you see how huge that grass is going to become. In spite of people saying you must move it away from the fence, it is much too close to it and the bed it's in is much too small. One plant should not be closer than 3' to 3 1/2' to the fence. Also, there is no point in placing two like that. Isn't there another corner of the back yard where you could use it to balance out the overall scene? ...Or somewhere else? If you look how big and fat the plant is in my illustration, which I'm not exaggerating, you'll see that the current placement is not going to work out. If you want to add color in front of the grass, increase the bed size large enough to accommodate more plants. You could expand the bed either to right or left along the fence. Or you could make a quarter circle bed that goes from side fence to back fence, and encircle the entire front of the grass with a lower perennial. Hybrid daylilies might work out well as they take full sun, are easy, and can be very long blooming. Or, you could do annuals.

Thank you laceyvail and cearbhaill. Unfortunately the dirt area is part of the dog's running route. Down the middle of the yard, around the pine tree and along the fence line, which is why we were thinking of some sort of hardscape additions, with adequate drainage, but then realized the root areas would be problematic. Fencing off beds is possible. While she runs like crazy, she is not an agile jumper and 18" of fencing deters her. We could add the platform deck (mainly over the existing patio) and some additional planting beds (not in the main running path) to improve the look while leaving the dirt paths (add wood mulch/cedar chips) to make it a bit cleaner. If hardscape is not a good idea and grass or ground cover won't tolerate a dog, it may be our best option. Thx!