1) Yes. You can do a flashback to a point before the upgrade. I'm not sure if I've ever done it, so I can't point you to a doc, but I'm sure you can Google for it.
2) Like I said, not sure I've done it, so I'm not really sure of the process. I would normally restore from a backup. I'm sure you will be able to find some explanation in the manual.
3) You wouldn't. You would restore to the same SCN. You would need to restore the primary, check the SCN and restore to the SCN on the standby.