there are night time lights that give off a little heat. Lots of people use heat mats on the sides of the tank vs going under the substrate. Just point one at one end of the tank to give your frogs the choice to go to a warmer end if they want. The exo terra heat mat (rainforest version seem to do pretty good for dart frog temps. Once your viv is setup with some plants that have become established you can add your frogs and the viv will pretty much maintain itself for the most part. Spot poop scooping is good to do and what you don't see the microfauna and plants will break it down

somethings to consider

Know what kind of frog you intend to put in the tank first, because you'll want to build your viv to cater to them. With that size of a tank you could make a nice habitat for a group of Leucs. Some frogs do better in groups than others, others you need to keep an eye on your male to female ratio.

With a vivarium comes keeping the humidity right, so you'll need a method of doing this. Fogger or misting are the two typical routes. With that big of a tank i personally would look into a mistking automatic misting system. It's worth the money. if you were big into fish you know what kind of equipment goes into it to make it a stable environment.

Lighting. With live plants you'll want some good lighting. Bulbs with at least 6500K rating for your plants.

If you are doing dart frogs they really don't need much ventilation. Most people make the top a glass or acrylic top to completely seal the tank off (also helps keep the fruit flies in). When you have little to no ventilation you may have issues with the glass fogging up making it hard to view your pets. Some people fix this by adding a screen section above the front glass or installing small PC fans to blow air over the glass.

Feeding. With darts you're main staple will most likely be fruit flies. They are readily available online from places like Josh's Frogs and they are also easily cultured on your own. You'll also want to seed the tank with springtails that will provide continous food source for your frogs to hunt.

There's plenty of videos out there on several different methods on making a background. The simplest in my opinion is the Great Stuff coco fiber method.