Hello there and welcome to the forum!
White's were a good choice. I have three of them myself, and my first was also my very first frog as well and I haven't regretted it yet!
Your list looks good as far as I can tell. Just a quick note, in an 18x18x24 viv you can really only fit two White's comfortably since they tend to get quite large, up to 6 inches in some cases! O: So if you want to get more than two I would suggest upgrading to a bit larger of a tank. But you were right to go tall, White's are tree frogs after all. They love to climb.
For the substrate you're going to want to use something with coco fiber as the primary ingredient (not sure what ABG Mix is exactly, so if you've covered this I apologize, just want to make sure I cover you.). For this, Eco Earth, T-Rex Jungle Bed, Exo Terra's Jungle Bed, etc.
As for the sphagnum moss, it's alright to use, but in moderation. White's can be quite aggressive eaters and it is possible for them to ingest the moss and become impacted. What a lot of people seem to do is put a layer of moss over the coco fiber substrate and then cover that with some leaf litter. This way the moss is safety out of harms way for the frogs and it won't stick to them as they walk around.Well...mostly.
As for the night light: You can use Exo Terra's moon glo lights. They work very well to let you be able to see your frogs at night and will usually not disturb their cycle. They're a very dim purple light, and look very nice in a planted vivarium.
I hope this has helped you! If you have any more questions please feel free to ask!![]()