Can S3 Be Used with EC2 Instances, and If Yes, How?

Yes S3 can be used with EC2 instances:

Create the Amazon S3 File Gateway on the EC2 instance.
Create the VPC endpoints.
Generate the S3 File Gateway activation key.
Deploy S3 File Gateway.
Create the NFS file share.
Mount your NFS file share.

What is the difference between stopping and terminating an EC2 instance?

Stopping an instance is same as shutting down your machine and you can restart it and the persistent volume prevails. Terminating the instance is like destroying an instance, there is no turning back.

What are the different types of EC2 instances based on their costs?

On-Demand Instances: Pay as you go
Reserved instances: Commit for 1-3 years
Spot instances: Get unused instances on upto 90% discount.

How do you set up SSH agent forwarding so that you do not have to copy the key every time you log in?

Start the SSH agent in you local computer. Add private key to your SSH Agent. SSH into the Baston host and then you can access your EC2 instances fron the Baston host.

How do you configure CloudWatch to recover an EC2 instance?

Choose your instance and go to Actions-> Monitor and troubleshoot -> manage cloud watch alarms
choose create an alarm. Toggle to alarm actions and choose recover. choose other required options and create the alarm.