<Edit Note> It does look like there is a support for AES on PRPC 6 platform, I did find several articles over this. I'm still not sure if there is an installation guide though. Let me try to find that out!
I wasn't able to find the AES installation Guide. Have you already received the media (installation files)? I'm wondering if they would provide a ReadMe file along with it which has the installation instructions.
AES 3.4 and 3.5 (which run on 6.x) look to have been sunset, so you can no longer request the media. If you plan on setting up a new AES instance, you should do so using a newer version of AES and Pega.
AES 72 is the most current version of AES available. AES 72 runs on Pega72 and provides governance, monitoring and management features for Pega 5, Pega 6 and Pega 7 systems. There are alerts introduced post Pega 72 that are logged by AES 72 but do not create cases.
AES 73 will soon be available. AES 73 runs on Pega 73 and fully supports Pega Platform 5.4sp2 through 7.3.
As far as database space required, that depends on things like how many nodes are being monitored and how many alerts and exceptions are being thrown by those nodes so we can't really provide an estimate. As a starting point, see what the installation guide for that version of Pega says. For example, the 7.3 guide states: 10 GB minimum initial tablespace set to auto-extend