Point 1) If your workloads need High IO SSD for DB, then you should have Master Slave setup. Ideally 1 master and 2 slaves spread across 3 AZ's is suggested. Even if there is an outage on single AZ the alternate AZ's can handle the load and serve your High availability needs. Between master - slave you can employ synchronous, semi or async replication depending upon your DB. This solution is costlier.
Point 2) Generally if your DB is OLTP in nature, then Amazon EBS PIOPS + EBS optimized gives you consistent IOPS. A Single EBS Volume can provide 4000 IOPS and you can RAID 0 multiple volumes and gain 10k+ IOPS for performance. Lots of customers are taking this route in AWS. Even though you may use EBS for persistence, it is still recommended to go with Master-Slave architecture for High Availability. I have written detailed articles on this topic in blog, refer them for more information.