We are a family of 3 hoping to use transit (and walking) for most of our 5 day visit to Seattle. Should we buy an Orca card? Is there any savings in buying a card, or is it just a convenience? It would be nice to not have to worry about change. Do we need to buy 3 cards or can we share one? And, if we take the light rail to one station, and then transfer to a bus right away, are we charged twice? Or is there a transfer time line? Thank you!