Using the same stepper motor drivers for two separate machines

Hey guys I am new to the CNC world and I am about to convert my x2 mini mill. I plan on using the monster kit for the electronics from Probotix as it seems to be the best deal with everything I need. Other than that I plan on following the plans off Hossmachine_Cnc Conversion as close as possible. While pricing out the parts I was surprised to find that the motors themselves were reasonably cheap so I started to wonder if I could also convert my 7x12 mini lathe to CNC with just two more steppers using the same breakout board and drivers for the mill. My shop space of course is limited so having only one controller box would be nice and it would also be much cheaper. Can anyone tell me if it would be possible and/or how to use one driver to control two different steppers at separate times meaning I would use the x and y drivers for the x and y on the mill or the x and y on the lathe. I am sure that simply unplugging one stepper and plugging the other in is possible however I would like some sort of switch to switch between the two since the electronics enclosure will probably not be very accessible. Also would I have to recalibrate every time I switched or will Mach3 store the calibration by the machine you tell it you are using rather than the hardware. Sorry for all of the questions but I also have to ask if ball screws are as necessary for the lathe as they are the mill. I am going to use them on the mill but the lathe seems to have much less backlash with its stock lead screws than the mill. Thanks in advance for any advice.