It will come with practices and depending on how you setup your constraints and drivers(In some cases). Since your constraints are based on the Luna rig then the Z axis needs to point upwards on the toe and foot. Otherwise you get the problem where it moves opposite direction. In your case the FK was correct so this would twist the foot and toes around when you switched from FK to IK. You can leave them as long as you leave all of them the same and then play with how each constraint affect them. This would require testing as you add each constraint to see what the effect is.
