I spoke with several of the team members back in November. You join during the second semester of plebe year, do not get to jump that year, and must remain on the team for the remaining years at WP. It is a very consuming sport, and due to performances/training, etc, team members miss many of the breaks that their classmates get. As far as getting on the team, they said ~300 plebes show up for the informational meeting, and after hearing exactly how much free time/leave they'll forfeit about 60 show up for the actual tryouts. The tryouts are very tough, and include (I was told) testing, PT (they smoke you), and at least one interview. About a dozen of the applicants are selected to be on the team.
Again, this information is my recollection of a conversation I had with 3-4 team members back in November, so I may be mistaken on some parts. I hope this info is helpful to you!