The estimate, based on number of physical agents, takes into account the 'virtual agents' that you see under the Custom Metric Host. In extreme situations, such as with a very large number of Calculators - there are some adjustments to make.
The recommendations in the docs are historically oriented to running CA APM on a laptop. For a production configuration, you should be thinking about 100-300 agents, over the next couple of years - unless you know that you will never reach that amount. This is the capacity of an Enterprise Manger Collector, in general. Just an aside, an Enterprise Manager has (3) possible personalities - MOM, Collector and Stand-alone. You are certainly in the 'stand-alone' configuration but just bear in mind that CA APM scales to hundreds and thousands of agents and monitoring components - when the opportunity presents.
However, the world view - from the SAP perspective (what they allow you to monitor, under the license terms), may actually be only 10-20 agents. So having a heap of 1GB for Introscope, with 2GB of total memory - should give you plenty to work with. It would probably be hard to configure a server with less memory than this!
Using the full capacity/potential of Introscope would require a 'full' license - which is something more than the SAP-RTV allows. So I don't see any reason to go beyond that because you are limited to the SAP-RTV.
As you get more operational experience with Introscope, you may certainly want to deploy it against your other application server flavors, or to take advantage of other CA-APM components. This requires a 'full' license, and you will need to contact a CA Account Executive to work out the details, in partnership with you SAP Account Executive.