Feather stone is (around here, anyway) an incredibly sharp lava rock. It is probably neutral as far as water chemistry, but it is so sharp I would not want it in a tank.
Look at natural streams and see what you are looking for. A few concepts:
Faster flowing water blows everything away that is not heavy enough to stay put. In a very fast stream (Hillstream Loach fast) the substrate will be rounded river rock, or cobbles, and smaller pebbles, but not sand and certainly not soil. A little sand or fine gravel might exist between large enough rocks that the current does not carry it away, but any plant that gets rooted there would get its leaves destroyed. The way to make this sort of stream work is to use mosses and algae that grow flat on the rocks, and small, very sturdy plants like Dwarf or Nana Anubias tucked between the rocks. Nothing tall, nothing streaming. Plants hanging over from the bank would likely have all their leaves stripped out.
Somewhat slower water, but still quite active might have some back water, a quiet spot hollowed into the bank or some similar protected spot that plants might grow pretty well. If the bank caved in there would be tree roots exposed. This could be done with cobbles, river rock, rounded pebbles at the front of the tank (perhaps cutting across at an angle) then a strip of planting area (not a straight line!), and 'driftwood' against the back wall to represent the roots. Plants might grow attached to the roots (anubias, java fern, bolbitis).