I've had a quick look for metrics in Cloudwatch and couldn't see anything but forgive me if I missed it. I would like to know if it's possible to watch and EBS volume and add more when it is nearing capacity. Is this something I can do through cloudwatch or should I write something to do it from the server itself?
Amazon has no visibility into how full your file systems are. You could write a short script to run within your instances, though, that could report this information to CloudWatch using their custom metrics.