1. I usually use layers of earth, them coconut husk, then a forest mix. Are we all good with this?
Definitely

2. I have a fairly good amount of sphahnum moss. Will we be using some (closer to when we will introduce the frogs) beneath the leaf litter layer?
I haven't used any and would love to know how my dart viv would benefit from the moss under the leaf liter.

3. The plants. Of course, bromeliads. What other suggestions do you have? Which ones should be seeded and which ones should be planted?
This is where I have zero experience. Found my ivy didn't like damp conditions so I'm gonna learn something here.