I guess I haven't posted an update in a long time. The plant, so far, doing the best is a brittlebush. As a bonus, it sheds old leaves as it makes more "branches," and the leaves are nice and crumbly and I can just mix them into the substrate. There are a few other grassy-looking plants that make these little flowers, and I haven't yet figured out what they are (I bought a few mixed desert seed packets). And I have two creosote seedlings in there too. The beetles are doing fine and eat mostly vegetable scraps from my own dinners, but I have given them dead bugs I find around the house, which they also devour.
The substrate seems to be settling a little on the side I keep watering, so I think I will need to make some more soil mix and add it. Again, adding an olla for my watering needs will probably help this, too.