The metrics which are visible under EC2 monitoring, like network, disk, CPU and status checks, are those sent to CloudWatch? If yes, where are they stored?
All the metrics of EC2 instances are stored and monitored by AWS Cloudwatch Metrics service. The default time interval of capturing these metrics is 5 minutes. However, you can enable a close watch upto an interval of 1 minute. This means Cloudwatch metrics can capture the metrics every 1 minute from the EC2 instance and display in the form of graph.
The graphs that you see in the EC2 instance monitoring dashboard are rendered using the Cloudwatch metrics data itself. You can easily view these graphs and several other metrics in the Cloudwatch metrics service.
However, Logs from EC2 instances and some other metrics like GPU performance and others are not really sent out to Cloudwatch unless you configure it to. You need to configure a Cloudwatch logs agent for the same. More details are available at this link