Welcome.

To design in a pond, the easiest way is to use eggcrate and create a square which you can then cover all the side with screen material to stop the higher area of drainage gravel from coming into. Then make a lower area of gravel inside the square. The drainage water that is filtered through the soil from misting is what makes up the water in the pond then. Just have some screen and stone come up out of the pond and over the substrate to stop substrate from falling into the water area.
The pond should then be only as deep as your drainage layer. You also don't want the pond deeper then the frogs can walk across since your darts are not swimmers.

Your darts will not drink from a pond since they will be absorbing moisture from the wet plants and high humidity your tank will need.

As for where the water goes from the drainage layer,.... depends on how much you need to mist or wet down the tank to keep the proper humidity levels. If the water collects and doesn't evaporate, then you need to siphon it off occasionally. I leave a corner with a little extra screen material so I can lift the screen and substrate and push a hose down into for quick siphoning.

As for lighting and heat. No special lighting is needed except for creating a day and night cycle or providing for plants. If your room temps are averaging 68 - 70 at night, then a simple Under Tank Heat Pad (UTH) on the side of the tank will raise temps slightly on that side and give a warn side and cooler side for the frogs. If you need to bring temps up at night then you'll have to check different lamps to get the right temps. usually a 40 or 25 watt will throw some good heat.
Adding a Compact Florescent (CFL) bulb with a color spectrum of 6500K for day time use (can get at Walmart under the Reveal Daylight 24 watt packaging) will raise temps slightly and be plenty of lighting for plants with the 6500K color temp. I run two 24 watt CFLs on a 20 long tank and have one T8 bulb to help with plant lighting also. Adjusting the height of the lights off the tank helps adjust temperatures.

You are also going to want to close up almost all of the screen material on your critter tank top. Humidity has to be retained and needs to be 90 percent on average. You are also going to have to make sure temps don't get to 85 or above for any length of time or your frogs will suffer or die.
My dart tanks are run at between 72 and 80 degrees. I have a very fine mist spray down the tank 6 times over a 24 hour period and for 15 seconds during each misting. I usually have to siphon off the hydroball drainage layer every other week.


Hope this get you a start and some ideas for your tank design.
Also check out some of the build journals since there are plenty with tons of pics to help with ideas.

Don