I like where you are going with this and I have a few comments.
I would be a bit hesitant to use the Ponderosa pine chunk ... I don't know how long you've had it, whether its been kiln dried, sealed, etc. but pines and cedars tend to exhude oils toxic to animals (plants too). Short of sealing the wood, I think it's safer just to steer clear of these woods.
As for substrate, have you considered ABG (Atlanta Botanical Gardens) mix? Many amphibian breeders, especially those who specialize in dart frogs, use ABG as the substrate of choice. It contains a lot of "chunky" material to prevent the substrate from getting compacted and promoting anaerobic decomposition. For a high humidity environment, I would suggest a layer of hydroton or leca, a sheet of weed block or fine mesh, then layered with ABG, and finished with a smattering of dead leaves. I would strongly discourage premixed potting soils unless you get some without added fertilizer, and definitely avoid perlite as it will stick to amphibians and causes impaction if ingested.