...1)
Is there anything else that's good to use for a drainage layer in a temperate paludarium-type viv that's 2/3 land, 1/3 water on a 12 x 12 footprint? (L. aurea) I'd rather not resort to large aquarium gravel...
Aquarium sintered glass bio-filter media (i.e.
Seachem's Matrix,
Ceramic Rings), or similar porous pebbles.
2)
I plan on a raised dry-land layer (or two stepped layers if possible). If I can't get egg crate, can anyone suggest an alternative?
Check hardware stores, electrical and lighting supply places for eggcrate (originally it's a light diffuser on 2x4 ft. fluorescent ceiling fixture). Alternates are under gravel aquarium filter plates or could get a polycarbonate clear sheet and drill drainage holes to it.
3) Is there a safe(r) way to culture slaters/isopods from wild-caught? I have no idea how to go about even trying to get springtails (wanted more for bio-system/clean-up than froggy feed source).
Try and find another vivarium owner that could give you some from a healthy tank. If none and you can collect your own in a pesticide free area do so. Let tank settle and cycle for at least 30 days without frogs and you should be ready to go.