Hey, late to this thread. Been lurking but have failed to respond.

- Leca - Be sure to hide a tube (PVC works great) in the spray foam background so you can syphon water out of the drainage layer. It will make your life a lot easier as time goes on. You can then stick a small tube down the PVC pipe with a sponge on the end of it and syphon the water out. Leca is usually recommended to be 1 - 2in, but you need to be careful with the small tank height that you don't chew up 4 or 5 inches of space with the substrate. You will also need to keep in mind that if you are going to do a small pond the Leca layer will need to be a bit higher than the top of the waterline to keep the water from swamping the soil. I would recommend against a water feature in the tank to conserver space, but that is just my 2 cents.

- Lighting - 9W for a 12x12 should be plenty.

- Spray Foam - Keep in mind it will expand so be careful how thick you lay it on. Anything you do will shrink the usable floor space for your little frogs. Keep in mind if you add 1 to 2 inches to the back wall you have reduced the floor to a 10x12 square. If you then do a 1 to 2 inch water feature then you will be left with a 8x12 square. If you add foam to the sides you could end up with a 8x8 square which is to small for even thumbnail frogs. You could consider doing a planted terrarium and using some wood to create hight and tie bromeliads to them.

- The Mistking will be a huge overkill to the tank. I love my mistaking, but in a true dart frog tank with near 0% ventilation the humidity will stay high and you will really only be misting to keep the plants growing. I use a hand mister on my Dart tank and my Mantella tank. The humidity in both stays very high all the time so misting them once in the morning and once right before lights out is perfect.

- Wood - I love the wood selection at NEHERP Give them a look. Ghost Wood, Manzanati, Malaysian Driftwood, and Cork Bark all hold up in high humidity. Grapevine is awful and should be avoided in humid tanks. They will mold very quickly. Cork bark will develop white mold nearly instantly, but it is normal and will clear up after a few days. The Driftwood is by far my favorite.

- Heating - There are a lot of options out there. My Favorite is now using Aquatic heaters, but in your setup a Ceramic Heat emitter will work great. It doesn't dry out the air, provides 24/7 heat without generating any light, and are cost efficient to use. You can use them in conjunction with Zoo Med Hydrotherm.

Sorry for the information overload. I'll answer any questions you have that I can and can't wait to see how the build turns out!

Paul