Wow thanks for the quick responses! I do have a hydrometer/thermometer. The humidity has been good, I mist once a day and it's holding steady around 75-80%. I gathered as much about the moss and that has already been removed

As for the light, right now it's a very low wattage but the temperatures aren't high enough (only around 74 F now) so I guess adding the heat lamp is the way to go. I have a 15W UVA light now on hand (I also keep hermit crabs that need much the same temp/humidity) - will that be a good choice or should I get something with no UVA? The light is on a timer so he does have a day/night cycle, no nighttime light right now though.

The live plants are in small glass containers tucked into the corners with riverrock and water, just covered by a little substrate. If they don't make it that's fine, but for now they're doing well

I hadn't considered the issue of the tank being too large - had assumed he'd just be happy and grow into this one. I'll keep a close eye, for now his stress levels seem low. The tank, as you can see, has a lot of cover so hopefully he feels secure.

On and when you say cover three sides, I'm assuming for the frog's sake? (lower stress). I do have a cover on the tank btw, that wasn't on when I shot the photo. Currently there's plastic wrap over about half of the space and then a mesh cover over that.