With (currently) 19 A340s on strength and a further 15 to come (plus options), as opposed to 14 B744s with none further to come, it will not surprise you to learn that the vast majority of Virgin's recruiting is for the A340. There is some movement on the B744 as people move from that to the Airbus on command promotion, but it's not a lot. You will not be given a choice; you will be told what aircraft you are going to (if you are successful).
As for hours, you will find that most pilots accepted in the current recruiting drive (which has been going on 15 months or so) have in excess of 4000 hours, and most of that on jets of 25 tonnes or greater. While the company's minimum stipulations aren't so demanding, the competition is strong, and the company can pick and choose from a very experienced, high-quality group of well-motivated applicants. In other words, a lot of very good people don't get in even though they have lots of hours. Them's the breaks.
Scroggs