While ancient walls have been built like yours and still stand, Marcinde's method makes it easier to guarantee that you won't have problems. Your wall looks like it has decent batter, but it cannot be determined from the picture if it's consistent throughout. I think this is one of the most important components of dry-stack retaining wall stability. Keeping batter sufficient throughout will help wall longevity. With greater batter comes greater stability and, personally, I like the look of it as long as it's uniform. You could easily create a wooden triangle with a level attached to gauge the batter uniformly.

The terra cotta walls and bottom are gas permeable, which means they allow water vapor to pass through the walls. This dries the soil faster and helps air return, which helps to reduce the negative impact of to heavy soil that doesn't want to drain. It also allows foil, growth inhibiting gasses like methane, CO2, and sulfurous compounds that build up under anoxic/anaerobic conditions (soggy soil) to escape through the container walls. Please don't take what I say as argumentative. I WANT you to do well, so I'm still going to encourage you to try to understand the principle of perched water in containers and how it is affected by soil particle size. Even if you only use the info to help you deal with heavy soils, it's better to have knowledge on your side. It only LOOKS daunting. Most people get the concept right away. It took me a long time before I could say this because it sounds like I'm boasting, but I'm really not: Literally hundreds of people, both newcomers to container gardening and those that have been gardening for a very long time, have said in so many words that "Now I finally get it. Now I understand why I was having so much trouble growing in the soils I was using ....." and so on. One way or another, you'll have to deal with the fallout when using heavy (water retentive) soils. I, or others here, can help you avoid the issues by helping you build a soil that better suits your application, or by offering tips that can at least partially reduce the negatives you're dealing with. Drainage layers or gimmicks aren't going help, but tilting your containers after you water and using a wick can help considerably - it's in the link I offered. Good luck. Al

Update: Well, I took your advice, and kept looking. I think I wore DH out, because he finally just said I could go and he'd be ok w/ whatever I selected. Freedom...yet a big responsibility so I need to get it "right"! So, the other day, I decided to dedicate a whole day to visiting other granite yards within an hour's drive from here. I walked into the first place, and saw a slab I'd never seen before. It is so different from the Giallo Ornamentals and Delicatus slabs I'd been "focusing" on, but I think it is THE one! It isn't quite as blue as it looks in the picture, but it definitely compliments the blue fabric on the dining room chair seats. (When I saw it, I realized that having gray/blue in the stone could work really well because we are opening up the kitchen to the dining room and our dining room.) It also has some taupe/neutral shades that work with the plank tile floor. What do you think?!

I thought this rug might look nice with the colors you suggested. I don't know if you ever used the site overstock before but it's amazing! I've purchased quite a few things from there, and am purchasing rugs for my own house from the website pretty soon. They generally have the best prices (because they get the overstock from other companies) and no matter what you get, the shipping is always 3 bucks! If you don't like the rug I posted in the link, you can just type in "flat weave rug" and you'll find a bunch of results. Here is a link that might be useful: Contemporary Rug