Are you talking with the 'dirt' space up, or laying the blocks on their side and stacking vertical that way.

Dirt space up... I hadn't even thought about sideways.

I think that you will find a lot of varietals that will work in that space, but you'll want to also plan on watering requirements. You don't want thyme on the bottom where it stays too wet. But mint or parsley would be happier with more water. Maybe half for the arid types and half that you water more often?

Most thymes work in that amount of space. They would probably even work sideways, though you would have to be very careful with the drainage, since they need very well drained. I think a small rosemary would also work, similar in drainage to thyme, and in 5b like me, it's really tough to overwinter rosemary, so it could just grow for the season, then pull and dry it or keep potted indoors for the winter. But, it does depend on how rosemary grows for your location--here in CO, it does not grow fast at all in our conditions. Maybe one of the draping, creeping rosemary types would be really fun to try.

Mints, I would check which types. My fav is apple mint which does get really big and probably wouldn't work as well. But my chocolate mints have so far stayed a lot more compact. I'm sure the bricks will contain them to a point, but they will go through a lot of water in that small of space. The runners will definitely go down and out the bottom if they can, so maybe some plastic or weed block on the underside of those sections could help.

Basils you'll want to check the varieties. The large leaf types probably need more space, but something like a fino verde or marseilles could probably work. I'm not sure about tarragon--it might if you keep it well pruned. I have never tried, but maybe mexican tarragon may be a smaller plant, since it's really a marigold. You didn't mention chives--those would do well in that space. Parsley or cilantro would also probably do fine, just pick several different bricks and sow one at a time weekly, so you get a little ready each time. I would also consider some edible flowers like french marigolds or nasturtiums, and pansies/violas in cool season for some color pop. Also, sorrel, summer savory, and purslane. Some of the lettuces could work as well.

My thought is that lavender and sage will require more room. Maybe block of a larger space with the small spots on the edge for a couple of the larger ones. I really don't know about oregano--hopefully someone else can give you a hint on that one. But most, it doesn't hurt to try!

I wouldn't put mint into a cinder block. They send out roots and the block wouldn't contain them. You will find them on the other side of your driveway and in your lawn!

Mint must be contained in a container with NO way out.

Might work if you set the block on concrete, like a driveway or something.

Suzi