Cool, what kind of ferns would you have on the rocks? Bolbitus, some kind of java fern or something else? A lot of ferns grow very large so they may look too large in a small tank, but I'm sure you can prune them.
Quite a lot of light for such low-light plants, but I gues you're having some stem plants too.
I'm just thinking is there such need for a substrate like aquasoil for a tank with mostly plants which attatch to wood and rocks? I would personally save the money, stem plants can also get all their nutrients out of the water.
I'm looking forward to this tanks progress.
Cheers,
Mike