Hi and welcome!
I *highly* recommend reading carefully through our caresheet before you go too much further. It will tell you everything you need to know:
Please check out our caresheet
CLICK HERE for CARESHEETIt's very important to get your basking temperatures right (and have a proper thermometer) and get the UV source correct and close enough.
If you put the viv you describe on it's side it would be a great size. Bearded dragons don't climb much except when they are babies, and even then they are very clumsy and could fall and hurt themselves.
If you were to use that viv standing up it would be great for 3-5 geckos (such as the crested gecko).
Not sure if you can put that on its side.
The minimum size is a 40 gallon breeder tank which isn't that tall but has lots of floor space
Dimensions are 36"Wide x 18"Deep x 16" High
Even though you could just not put branches into the tank you have ordered, you would have a big problem with getting the UV light close enough and the