The waterfall looks awesome! You can use pothos for the vine and java moss for the land( it won't get long as long as you have something in the tank to trample it down, but if you don't keep it under control, it might take over your tank ). I definitely wouldn't keep it
dripping wet(that causes mold), but it all matters on what you put in there, if its dart frogs, then it should be moist(yes, a small fan would work if you have something that causes very high humidity, like a misting system, but other than that it would be fine without one, i would think).

Also, acrylic scratches easily, but you can drill into it without too much trouble(if you need to for cords or tubes), it can also
easily be scored and cut, unlike glass. But, glass doesn't scratch as easily, is easier to clean IMO, and many people just think it looks better. I personally use acrylic, because I dont have the tools for cutting glass, glass is usually more expensive, and I'm always afraid of breaking glass, lol.