Small catfish would be fine:
Otocinclus
Corydoras
Farlowella
Ancictrus
Parotocinclus
These would all work in a heavily planted tank. I know.
Panaque is getting too big. Anything bigger than that is much too big. Flourite would be much too rough for a Panaque, or IMO most bottom-dwellers. Did anyone say this, yet?
People who go in for natural aquariums have been using topsoil, and they know what they're doing. They use it with a covering of gravel, and they keep mostly livebearers, and fish that don't dig much or eat plants.
There is more than one way to do it.
Sometimes they keep the plants in pots, to protect them from boisterous fish. Topsoil in the pot, covered with gravel.
It is a whole other topic, and a whole other field of endeavor. There are many websites that specialize in information for this kind of tank.
I think topsoil
and Flourite is overkill, but so what? They don't work against each other. Just keep those stem plants in there! As thick as you can!
If I had seen this post when it first went up, I would have said don't worry about the Flourite - it
always settles out. Don't overrinse it, either. You need the "fines" to enrich the iron delivery.
Excellent job, Catfishmutant! 
Deborah