Nice video. Keep going... Perhaps you could experiment next time by combining the so called ICM approach with Multiple Exposure Mode. For example, your "hyperdrive" with fixed exposure or so...
It really depends on how slow a shutter speed you want to use. If you get a variable ND filter that goes from 1 to 6 or 7 stops, you should get some great results. If you want to use normal ND filters, I'd go for a 3, 4, or 5 stop filter. It's entirely up to you. You can get great results without an ND filter. Just shoot early in the morning or late in the day when there is less light.
