That is not really a true “rule”. It was a firm suggestion in the past, but for SOHO, (basically most people here in the forums), we routinely discount that suggestion without real issues.
Of course, more RAM is better, but does not always help in all cases.
Again no. Their is no “virtual memory/pagefile/swap” in TrueNAS SCALE, and L2ARC is not for that purpose.
L2ARC is a secondary cache for the ARC, (Adaptive Replacement Cache). See this;
