Are you looking for historical data such as you would use to make a chart? If so, you are looking at the right entities.
You can get last 24 hour CPU and Memory utilization with a query like this:
SELECT CPULoad.Node.Caption, NodeID, DateTime, AvgLoad, TotalMemory, AvgMemoryUsed, AvgPercentMemoryUsed FROM Orion.CPULoad WHERE NodeID=2 AND HOURDIFF(DateTime,GETUTCDATE())<24
Similarly for traffic in/out and Orion.NPM.InterfaceTraffic. On Orion.CPULoad, "Node" is a navigation property. It gives access to the properties of the associated node. In my query above, I used it to get access to the "Caption" property of the node. It is short-hand for a JOIN clause.
Hope that helps.