Man, how relieved I am.
I was checking into that 8.3 (DOS era legacy.. seriously McAfee ??) thing and found out that ePolicy Orchestrator directory didn't have 8.3 name.
Which explains why there were "ePolicy Orchestrator not found" kind of errors in some logs, while the directory clearly existed.
I renamed ePO directory, created new directory ePolicy Orchestrator in Command Prompt, checked that it has a 8.3 name now by using dir /x in C:\Progra~2\McAfee.
Where McAfee support was unable to help me, Apache logs pointed me to correct path.
After having done all that, the McAfee services started and the site was up again !
I will make a snapshot of the VM now every time I'm going to upgrade Let my fail be a lesson to all of you who think that what's the worst that can happen