are you going to have the water come along the sheet of metal and then down the hole - where the paint stirrer will be spun ?
don't want to rain on your parade.... but you'll get a lot more power if you mount the paint stirrer inside a length of pipe.... even better if you have a larger pipe, and then reduce the size just before the paint stirrer.....
the water has a lot more momentum inside a pipe that it does falling through the hole in the sheet metal....
edit:
bit quick and dirty, but here's a diagram to show what I mean....
if you have decent fall after the turbine, you can extend the exit pipe so more water is syphoned through.... add more "head" to the system...
(same goes for the incoming water)
