Idea for a setup
 

Rings any bell to you?

https://ae01.alicdn.com/kf/HTB1VCogL...font-water.jpg

And this one?

https://sc02.alicdn.com/kf/HTB11yPnL...i-Fountain.jpg

A little bigger...

https://sc01.alicdn.com/kf/HTB1CzaGF...door-Patio.jpg

Instead of a closed/semi closed terrarium why not construct a wall of some non degradable material, maybe with some terraces, install a small pump to get water from a small container and, by means of a piping, make it fall by that wall. Install some suitable plants on the terraces and, ideally, one just need to refill the container...:hmm

Just an idea that came to mind when I remembered these small fountaing used for decoration.

Rbarata, cute idea, minus the happy frogs.

If they were alive, at least, I would keep them.

Although I find a terrium/orchidarium project an interesting and fascinating project, I also am aware that if has all the potential to be a source of frustration and concerns.
It might be a misconception of mine but that's how I see it. The environment inside an enclosure it's so fragile that finding and keep the balance between a success and a catastrophe is something really hard and needs constant monitoring.
Orchid growing should be something pleasant and start such a project without the right conditions to keep is something with a high probability of faillure, which is not a good thing.
As far as I know, air circulation and temperature rising are the main factors for faillure so keeping the enclosure out of the equation increases the probability of success.
It might not be suitable for certain species but it will be for others.

I think it's a good idea. Go for it. You are super creative any how! Maybe look for orchids that grow at streamside.