Rich media is more of a bandwidth issue.
Current advice is to allow 40 MB per PHP process, times 500 makes 20 GB. With 16 GB you are roughly there, unless the 64 bit PHP consumes more RAM than the 32 bit version.
I am not familiar with VMware ESX. If I understand right, it is the hyperviser, sort of big virtual hardware on which you install your familiar operating system: Windows or Unix. On top of that comes the AMP stack (webserver, database server, PHP), and finally Moodle.