Those plants are going to be way tiny, I can promise you. Imo if you have any kind of garden center nearby (Walmart, Lowe's, home Depot, anything) go over there and look at some plants in person. They will have a whole range of sizes and plants and you can spend a few minutes holding things next to each other and trying to visualize how they'll look in your setup. If you have even the 18x18x36 cage, those plants are not going to fill any space at all, and if you have a 24x24x48 they're definitely not going to cut it.

If you can't get to a nursery near you, I recommend looking on Etsy for plants, or at least try finding some for sale on Amazon that are a little bigger. Also, if you can't find a taller standing plant (like your schefflera) then try getting a plant stand to help it sit higher in the cage and not on the floor where it'll be too low to be of much use. I have this one For my shorter standing plant and it works really well.