We've worked closely with our team at AWS to ensure we are following best practices. The consensus has been that 4+ AZs and 12 instance types is sufficient dive

We've worked closely with our team at AWS to ensure we are following best practices. The consensus has been that 4+ AZs and 12 instance types is sufficient diversification. We also have a second, on demand, ASG ready to fire up at a moments notice if something were to happen with capacity. We also heavily leverage managed services for state.