When an agent starts it will perform a full discovery, if the EAP server is not running at that time it will be missed. Discovery runs only intermittently because it is intensive, and in general nothing is discovered. Assuming your RHQ server and agent are running, you can always force a full discovery by executing the "Execute Prompt Command" Operation on the RHQ Agent resource (assuming you've already imported the agent resource). As the prompt command execute "discovery -f". This is useful to force discovery of a server that has started up after the agent is alr3eady running. Then you go to the Discovery Queue (under the Inventory menu item) and you can import the newly discovered server. It's child services will then be discovered and imported automatically.
As for metrics, out of the box RHQ metric collection is conservative so as to not waste time and space collecting data that isn't interesting to the user. But for a demo you can go to the resource you're interested in, under Metrics->Schedules you can enable and disable metrics, as well as set their collection intervals as low as 30s. Pick a few and set to the minimum interval and you will start to see data coming in much faster.
In general I'd just get things imported and collecting quickly in advance of the demo, but if you need to show those options then you could do that too.
Thanks a lot, it works!