re: Speed and Distance
The official cruise speed is 2 cm/sec, but pauses and other things required for navigation deliver an actual average of 1 cm/sec, as Nick says.
I have high hopes for these rovers. NASA has a long history of its probes wildly exceeding their planned "design lives," and we could get lucky again. We may eventually get out a considerable distance from the landing point, but as Nick points out, there are enough things to look at that the mission planners could find plenty to do and learn in the area nearby.