Network throughput for an Oracle database : Smaller number of large PIOPS volumes or large number of smaller PIOPS volumes

Individual 4000 PIOP volumes at 16K  I/O's can theoretically transfer 64MB/s.  Smaller PIOP volumes (e.g 1000) can burst up to 40MB/s.   In this case, especially for bursty workloads, it may be more cost effective to use smaller PIOPS volumes (but more of them) in a raid0 configuration, than to use fewer higher rated PIOPS volumes.

Oracle on AWS - EBS mirroring

Question RAID and EBS Raid 1 - Does AWS EBS provide recovery from an EBS volume since the data is automatically mirrored by AWS?

Response:  It depends on whether  you want control over the recovery for mirroring.   Using the built in mirroring means you do not control the mirroring and therefore when recovery happens.  Other options include using Oracle Standby DB/DataGuard, GoldenGate or even EBS snapshots.