The water proofing is more so the wood will be able to hold up to humidity and damp conditions rather than standing water. If you have built wood enclosures for herps before I am sure you can work something out.
Yes, as long as they are similar in size, they will try to eat anything significantly smaller than they are.Would it be safe to keep multiple together?
Feeding some mealworms is fine, as is feeding crickets, feeder fish would not be likely to work though. I would also recommend getting some repashy ICB to dust the food with. It is probably the best choice in supplements on the market and can be purchased online or at some reptile shows.I have mealworm colonies to feed my gecko, will toads eat these? I can feed these as well as feeder fish and crickets. I plan to try breeding crickets so food shouldn't be an issue.