I wanted to post an update to this build: I have added additional layers of light diffuser onto the backdrop, and reached the level of brightness I am looking for. I am also up to 30 unique plant species in the enclosure.
Someday I'll set up my DSLR and mess with the lighting and camera settings until I can get a really good shot (the backlight looks really good in person and not very good on camera). Until then, here are some iPhone pictures.
Macodes petola and Cryptanthus
Ludochilus "Sea turtle"
I have a couple more plants in my grow out I am going to add, and then I'm looking to put in 1-2 epiphytic orchids, but after that I think I'm basically done planting and it'll just be about maintenance and letting everything grow in the way I want it. I am trying to encourage my various vines to grow over the climbing branches.