It's a bit low. They recommend 7V+ for a reason. You lose 0.7V in the reverse polarity protection diode, and then the voltage regulator has a 1V dropout. That is, it needs 1V headroom. So really you need 6.7V upwards, which is why they say 7V to 12V.
So you are saying just have 2 (or 3) LEDs go on at once, then the next 2 (or 3) would go on as the previous 2 (or 3) shut off and so on to create the chasing effect?
Yes, I think groups of two chasing would look OK. You could try it and see. Failing that you can use a shift register or two and put 8 LEDs per shift register.