Ah, Novus. Gotta love that stuff!!! I'm sure you'll have that thing clear soon.
For your substrate question, the trick is rinse, rinse and rinse prior to dumping it in. Even the pre-rinsed stuff. Coarseness depends on what sharks you want to go with. I use pretty heavy large grain aragonite on my bigger tanks to keep it on the bottom and out of the filter/water column.
I'll be honest, my first thought for a species was grow out for Japanese Smoothound
Triakis scyllium (AKA Japanese banded hound shark). Those guys are so amazing and you just don't see tanks with this type of foot print for them to use properly. Atlantic guitarfish would be awesome in there as well. A tank this rare looking almost requires a cool rare elasmo to live in it.