When the user account has reached the maximum number of EC2 instances, it will not be allowed to launch an instance. AWS will throw an 'Instance Limit Exceeded' error. For all other reasons, such as
"AMI is missing part", "Corrupt Snapshot" or "Volume limit has reached" it will launch an EC2 instance and then terminate it.
Reference:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/Using_InstanceStraightToTerminated.html

Explanation
S3 One Zone-IA is a storage class that is designed for data that is accessed less frequently, but requires rapid access when needed. Unlike other S3 Storage Classes which store data in a minimum of three Availability Zones (AZs), S3 One Zone-IA stores data in a single AZ and costs 20% less than S3 Standard-IA. This storage class meets the requirements of the company because it provides a low-cost solution for the secondary copy of its on-premises dataset that would rarely need to be accessed. The other storage classes are either more expensive or not suitable for infrequently accessed data.
https://docs.aws.amazon.com/AmazonS3/latest/userguide/storage-class-intro.html

A subnet is a range of IP addresses in your VPC. You can launch AWS resources into a subnet that you select. Use a public subnet for resources that must be connected to the Internet, and a private subnet for resources that won't be connected to the Internet.
To protect the AWS resources in each subnet, you can use multiple layers of security, including security groups and network access control lists (ACL).
Reference: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Introduction.html