1) I wouldn't hold my breath for SQ to ever let anyone use the upper deck!
2) Standard "crew meals". There is no prohibition on taking anything you want, although it would be a little tough for a 15 day trip!
3) Standby down line? It's realy hit or miss. Some people lead charmed lives and never get called and then again, others aren't too lucky. It really depends. It's really only used if someone goes sick or there is a massive reschedule.
4) Oven training? Most of the F/Os will take care of the cooking. But if you can open a door, turn a timer, you're qualified!