I've created a couple of these - one on a test rig and one permanently which became a KITT type Larsson scanner. To run multiple strands I'll be putting an ATTiny85 at the top of each with Vcc and GND shared across them from a wall wart. While they'll run independently, the slight randomisation in the speed and delay between falls should create a reasonable effect across the windows at the front of our house.
Measuring up the 4 windows I'll be running these in leads me to think I'll need 30 of them, so 600 white LEDs...the project is approved by the minister for finance and war so it's just a matter of sourcing the bits and dedicating the time. I'm actually very happy I have a 10 month project window on delivering this one 
Geoff