>> Is it possible to do these backups in a way that would have all the flashback >> stuff on one array and the backup sets on another?

Yes, definitely. I believe you can put the flashback logs in the flash recovery area, but you can have RMAN write the backup sets to any arbitrary path, so they could be written to the other storage array.

You also mentioned that you have 544 tablespaces and that you are a data warehouse. Does that mean you have a lot of range-partitioned tables that are loaded once and not updated? If so, make those tablespaces read-only then back them up with RMAN. Then they won't affect your backup time, because RMAN won't need to back them up.

Incremental backups are definitely a winner, make sure you use the block change tracking capability.

The combination of incremental backups, compressed backup sets, backup optimization (see the documentation on that one), and read-only optimizations should reduce the footprint of your backups on your operations.

One other thing, I would be wary of putting the online redo logs, archived redo logs, and flashback logs on the same device/disk/volume. You could be setting yourself up for some I/O contention issues.