1. upgrading the firmware fixes bugs, improves functionaility and overall stability
2. no - you need the maps on a disc to copy them back on in case of failure
3. all Version C will often give battery drain as they come from factory with 2660 which started it all off. A K gateway (providing its a later one) will have no problems. Cs are not downgradeable below 2660.
Downgrading the firmware can lead to instability, loss of functionality etc
You also need the latest firmware to get the latest features in the maps, such as speed limits, further POIs etc.