Hi Jeremy and welcome!
Some answers - the data for flight info from the network is refreshed every 30 seconds - there's a countdown timer at the bottom of the screen. It's not changeable.
Fo flights that you are picking up locally on your RadarBox and from the network, the data is first searched for on your local database, NavData.db3. If it's not there, then, if you click on the flight in the grid or on the map, RB will look for it on the AirNav server. If it's not there, AirNav will search for it on the Gatwick Aviation Society (GAS) database and try to get pictures from the Airliners.net website. This happens whether or not you are chosing to get network flight info.
As for the CPU demand, that rather depends on which version of the RB software you're using. It's less if you are using the Version 3.0 Beta version than if you're using Version 2. My CPU's currently (and it's late at night with not many aircraft around) using between 7 and 20% CPU, peaking every 30 seconds (when the network data arrives) at 60% for no more than a second.
And it shouldn'tbe using much RAM, no matter which version you're using, or which Windows version you have. On my system (Version 3 Beta on XP sp3), it very rarely uses more than 640 Mb of RAM even though I've got 3 gig.
Hope that helps.
Rod