The train still stops at Noarlunga - and will be leaving Seaford every 7/8 minutes during the commuter time in the morning - Noarlunga is the next stop and they will all stop there. Its slow, but very regular so you wont have any worries about rocking up at Noarlunga and getting a train. If you are like me, and get a bus as well, it gets a little trickier to tie up buses but Christies is quite well served by buses I think.
If you have a smartphone, there are a couple of apps - I used TripMate Adelaide which cost a couple of dollars but downloads the entire Metro timetable and you can specify fav stops \ routes etc for quick viewing. I think there is a free Metro app too.
There is an active Facebook group called Noarlunga Line Commuters 2013 which is good for the latest gossip and news - you get better info there than from Metro themselves!