Welcome to Frog Forum, Nanafish !
You will be able to get lots of help here. WARNING !, WARNING ! This is a very contagious hobby.
It is great you arr setting things up BEFORE getting the forgs. "Reading" and learning will really help you!
However, a quarantine period is needed as well - If you get more than one and they are 'together' then they can be in quarantine together.
If they are very young 'froglets' the quarantine in important to monitor their food , poop etc ( get to know them !)
A FF search will provide lots of information of what a quarantine enclosure should look like.
23" tall is nice--- for red eyed tree frogs -- the taller is better!
You will need heat if you can not maintain the necessary temp. parameters. A good probe thermometer is a must.
( I actually us a battery operated ,exterior ,weather station in my tree frog enclosures) Heat cables? Up to you. I use a 6' foot one outside my enclosures/ 2" under the glass! In my experience with these, I would NOT put it in the tank.
YES a day/night light cycle extremely important, It is very important you read more about this to understand how to take care of them properly.
Substrate does not have to be fancy. They really don't care about it . They only come down at night to eat. Read about bowl feeding, I think it is the way to go, as it is very important to monitor the food intake. Loss of appetite w/ these frogs is a sign of trouble. I would avoid moss ! You don't want them to swallow it risking fecal impaction . Yikes !
Plants, plants, plants. Start now----- lots of suspended big flat leaves. The will eventually sleep on these and feel secure there. Read about preparing the plant before they are put into the enclosure! After being re-potted ( and a waiting period) ---you can plop it right into the enclosure in the pot.
Check out member's albums for ideas!
Humidity is very important. An acrylic lid will likely be necessary. Mister or fogers are great. However, hand misting will work if you have to put off that expense for now ?
De-chlorinated water is a must ( for their soaking dish ) cleaned daily /chin deep
Distilled water is okay to clean the glass and for misting- and will not build up on the glass as much. The frog(s) should not be sprayed..
Small feeders, even for adults--- using a calcium and vitamin supplement on regular schedule .... a must.
Avoid handling---- This is NOT a frog to own if you want to touch it !!!!! If it is necessary, clean damp hands ( powerless gloves) . And wash your hand when you are done !
I would have to say the most importing thing to remember ( for red eyed tree frogs) in my opinion is..... keep it CLEAN. Most illness occur form dirty enclosures, calcium deficiencies, and stress due to an improper set -up.
It's a start
Hope this helps !
Lynn