SectorSafe I'm sorry, I don't know how full the hold pool is right now. I suspect that it's kept topped up as people are drawn out for training, as Virgin continues to require a healthy supply of new pilots for the forseeable future.
As for which type, a read of this thread will reveal this question has been answered several times! Virgin is buying 25 or more A340-600s. It isn't buying Boeing 744s. The answer ought to be reasonably obvious! Inevitably, there is some internal movement from the 744 to the A340 as people reach command, and as those 744 skygods (well, they say they are!) who wish to fly the A380 in the future transfer to the A340 to get some Airbus exposure (a company requirement). Therefore there are a limited number of vacancies on the Boeing, but the majority of the requirement is to fill the A340 slots.