I don't know why people think there is some standard set of known values for these kinds of things. They just don't exist.
Why? Because everyone uses Liferay differently.
For example, Sesame Street and the Marines use Liferay. You can't pick two completely different use cases. One is serving games and contents to children while the Marines, well lets just say they are not doing that.
They'll each have completely different memory foot prints, performance, JVM parameters charts, configuration and even hardware.
You build out specifications based upon your own requirements and evaluation. Settings you pick for a 200-employee intranet vs a multi-million internet facing behemoth. Those things determine your hardware, your cluster size, etc. Your use of the doc library can determine disk storage requirements. Your concurrent user support and how good (or bad) your custom portlets manage session usage affect your memory requirements.
