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Eclipse and JBoss could have been put in the casdev HOME directory, but by putting them in public space /opt they could be shared with a second user if you created such an account. Assigning ownership to casdev makes it simpler to add options to Eclipse or to edit the standalone.xml configuration file of JBoss if you need to.
When JBoss is installed in DEV TEST PROD, production services has the licenses to use the RPMs, so different parts of JBoss are scattered into different parts of the system directory structure. For the most part, it doesn't matter if JBoss is completely unzipped into/opt/jboss/jboss-eap-6.2 or has pieces scattered around. It might be important if you want to start JBoss at boot time as a system service, but that is not how development is done. The one directory that matters is the jboss.server.log.dir (the directory into which JBoss puts log files). In production, this is /var/log/jbossas/standalone, but if you just unzip into a single directory it defaults to the log directory that you unzipped. This is changed by setting the parameter explicitly when JBoss is started in Eclipse.
The VM
The VM is a standard Virtualbox 64 bit Linux configuration. With JBoss running the virtual memory use gets up to 1.3 GB, so it could be reduced to 1.5 or 2 GB of virtual RAM if you need to run two VMs on an 8G laptop.
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