Callisto, the Flourite is fine, but it is expensive, too. The only downside for me really is the size of the grains and the color (I wasn't crazy about the brownish-red). You can get Eco-complete or Flourite in a sand version that I think would be better for hairgrass, if you're leaning that way, and they come in black.
My substrate consists of a tiny (and I really mean tiny) amount of peat on the bottom...a sprinkling. I then added regular Flourite that I rinsed well before adding to the tank. Finally, I placed about 1-2 pellets of Osmocote every sq inch of the tank under the Flourite. I poked holes with a wooden art brush handle and dropped in the Osmocote before I flooded the tank.
You can definitely do it without a soil-based substrate. The only other thing I did was change out my bulb to a Hagen 6500K bulb. The one that came with my unit had a very pink cast and to the human eye appeared to not produce as much light.
Good luck on your new tank! I'll check out your thread.