Virgin's initial A380 pilots are volunteers from the A340 fleet. B747 pilots wishing to transfer to the A380 will have to complete at least a year on the A340 first. Volunteers will be selected by seniority and will need to be able to offer the airline some 3 to 5 years of service once converted.
While Airbus flight decks are similar in the A320-A340 series of aircraft, the technology under the skin can be quite different - the A340-300 and -600 series aircraft are a case in point, where there are considerable differences in the flight deck switchery on some systems. The A380 is quite a different animal, though the Airbus flight deck and flight control philosophy is strongly evident.
Most long haul airlines use around 8 or 9 crews per aircraft. The A380, like other extreme-range aircraft, may need higher crewing ratios for many of its sectors.