Definitely enough space, Tara. Some people consider 12x12x18 the minimum for one adult, but it's more generally accepted that 18x18x18 is good for a single, and 24x24x48 is acceptable for a pair. The key is plenty of coverage- don't be shy! I was a little worried I smothered my crestie's viv, as they do enjoy space to jump. But cover is important, they need to feel safe. I'd suggest maybe another twisty vine, try entwining it around itself to make a wreath and attach one to the top for a circular, heightened, horizontal resting space.
As for hanging plants, just get the fake ones with the suction cups and attach the suction cups at the desired height. The ground isn't very important if your gecko has good mental health. I use eco earth for substrate for aesthetics and to hold humidity, but I've never seen my gecko on the ground (except the first day I put him in, where he went across the ground, then right up into the foliage). Keep their arboreal nature in mind when placing their feeding dishes as well. I place my crestie's water bottle cap of CGD on the bottom of the piece of grapewood I have resting vertically, in a sort of tree-trunk fashion with the aforementioned vine wreath positioned above it. From there, I entwined a Fluker's Repti-Vine around it to make it similar to a shrub.