Wawa:
A string of five LEDs in a segment uses 9mA (not 9mA per LED).Eight segments (7 + DP) * 6 = (8 * 9mA) * 6 = 432mA (0.432Amp)
A 12volt/1Amp supply is more than enough for six displays and the Arduino, even if you decide to use 100ohm resistors for the segments (higher brightness).
Leo..
Thanks!!!