Ideally you shouldn't rely on the linear bearings to provide the current path to earth, so earth both.

You can jog a specified distance by using the MDI tab and typing the Gcode commant, which is easy enough since you can see the co-ordinates the machine is at, so just type G0 Xsomething Ysomething etc to move to where you want. You can also set jogging to moving set distances instead of continuously, so for instance every time a jog key is pressed the axis moves 1mm (or whatever you set).