Lisa, the advice Bill and others have given you is spot on. I would just like to add that, when you go plant shopping, resist the understandable temptation to be overly adventurous and purchase more than you need, because you have lot less space than you think. Even though your tank isn't small (24x18x18 is roughly 34 gallons), by the time you have a false bottom/substrate layer, background, water feature, maybe a place for a feeding bowl and whatever decor you're going to have in there, the actual room available for the frogs to move and plants to grow is probably only half of that. And grow they will. Some of them like the aforementioned pothos can explode and block out the light in no time; others like the creeping fig like to extend themselves all over the place. Even slow growing bromeliads will produce offshoots. Not that that's a bad thing, but without ample space to expand, your vivarium quickly gets overcrowded and your plants will be forced to compete with each other for light and real estate.
The other thing, as Bill has already alluded to, is to prioritize your plant selection and vivarium design based on what your frogs need. Red eyes in the wild like to stay amongst the leaves and dense cover of the rain forest canopies, typically 100 feet above the ground. They rarely venture down to the forest floor, so while having a few terrestrial ferns and shrubs at the bottom of the tank would make for nice decor, they serve little purpose as far as the inhabitants are concerned. A lot of terrarium stores also tend to cater plant selections toward dart frogs, and these plants generally end up much too small and fragile and terrestrial for something the size of red eyed tree frogs - things like peperomias, pileas, etc.
Suitable choices, imo, would be broad leafed vining plants that will climb and fill up airspace all the way to the top of the enclosure. Red eyes also prefer to climb from amongst the foliage rather than hop, and they oftentimes sleep on leaf faces so having leaves and stems that can support their weight is ideal. Pothos and philodendron vareties would do nicely. Hoyas also make good additions, but their leaves tend to be smaller. Bromeliads are great because they don't require soil, allowing you to grow them anywhere in the vivarium. They also collect water, which helps maintain humidity. I generally avoid tillandsias because they tend to prefer lower humidity and greater airflow most of the other plants mentioned. They rot quickly if allowed to contact standing water. Orchids are also hit and miss - some can be really touchy...not to mention expensive.
I guess my suggestion here is to start simple: have a main course of a broad leafed vining plant like pothos and a couple of sides, with maybe a bromeliad or two up top. Then, once the terrarium has had a month or two to grow in properly, you can decide to add more plants if there's room or reason to. And stick to easy, "indestructible" plants. If this is your first vivarium project, there are going to be enough stumbles and missteps that the last thing you want is to lose that rare orchid while figuring out what sized pvc pipe to use. All this is from personal experience - I redid my first tank at least half a dozen times. Plant casualties were high![]()