Nokia C5-00 - I live in a 2G coverage area only, what will my experience with my Nokia 3G device and for example with Nokia Maps be like?

Going from 2G to 3G and vice versa, is a seemless transition. All data applications will still function. You may encounter slower data transfer speeds when in 2G mode. Nokia Maps will not be affected. The built-in GPS can be used even in offline mode when map data has been pre-downloaded to your device memory.