You need 20 points to order the card. I believe the card expires the december after the year you order it in (at least that's been my experience). Yes, you can order the card now and transfer points right before you leave. I think you have to have a min of 10 to do a transfer after you have the card.
The only warning is this - if your card expires, you lose all the points on it, so make sure you spend the points before the card expires!!!!!