You can store 6 base maps and 10 real-time maps on the AP.
I asked Cobb about a fuel economy map and the reply was "we're working on that, should be available in the near future".
The AP needs to be connected to the ECU in order to switch real-time maps but then you can remove it and the R-T map will function as long as the ECU is not reset.
I do not believe you lose anything when using a R-T map. The base map comes with program code changes, not just map data. A R-T map is apparently just map data but the features of your base map (like CEL activity, anti-knock, etc.) are still in use.