You can either backup the config via a SNMP manager like WCS or do as you did through the controller itself. In version 3.2 the configuration is binary so it won't be human readable. As far as the file extension, it just came down as .aes because that is what was listed in the filename on the Commands-Upload page. It really doesn't matter what the extension is.
Dan is correct in terms of the configuration file as for the IOS Image as you call it, I don't know nor have I heard of any way to backup the controller software image, but the controllers do have a primary and secondary image stored on them. From the CLI type "show boot" you should see something similar to this