Farming for Darth revan

So it's looking like I have a really good shot at getting Darth revan when he returns. I've been buying double refreshes on a daily basis for fallen bastila and Juhani and occasionally carth. But even with the double refreshes bastila still sometimes doesnt have the best drop rate. Is it worth it whenever I have the extra Crystal's to buy her shards from the shipments or just keep doing what I'm doing? And also when would it be safe to stop buying refreshes on the rest of the characters? Fallen bastila is 30/100, juhani is 67/100, and carth is 63/100. Then obviously hk is done and canderous only needs 4 shards. I just wanna mention that whatever Crystal's I dont spend on refreshes then are being saved for Darth revans pay wall gear so I can have him ready for the malak event just incase it follows afterwards. So again is it worth buy bastila shards from shipments and when is it safe to quit refreshing the other 2