If a person is piloting a viper, do they simply get 1 action (move, or fire) or can they sacrifice a skill card to move, then use their action to fire? Could Starbuck potentially use a skill card, then use her double action to fire twice?

When you are in a viper you still have 1 move and 1 action. So you can move the viper and then take an action (or two in the case of Starbuck).

You only have to discard a card if you want to move from the viper to Galactica or Colonial 1.

Thanks for the clarification, and that's a serious duh moment for me with the 1 card discard. It certainly makes actually piloting a viper a lot more sensible.