1) Have a look at embedded Jopr. This is the new open-source admin console based on JBoss ON.
2) Are you asking about upgrading to new level/version of JBossAS? If so, then only way I know is a clean install of the new version, then moving over the apps and configuration settings, making changes and fixing issues as appropriate. There is no documented or formal migration strategy.
3) Some people use subversion or other similar tools to maintain configuration versions.