FYI, I never use rotation constraints on character limbs...using it for limbs literally limits the flexibility and posing possibilities for a character. During animation, Limb joint constraints can get in the way when trying to hit certain key poses, and can become more frustrating than helpful. Adding rotation constraints to the limb joints may seem like a good idea but it's really not that useful in practice.
Rotation constraints can be very useful for limiting the turning range for Smart Bone Dial controls. They're also useful in certain mechanical setups and specialty rigs. Just not so much for character limbs.
(Note: It's more common for me to use joint constraints for characters in 3D animation programs. But even then, I sometiems wind up breaking the constraints so I can get the character to do what I need it do.)
As for Target Bones for feet,
normally, I leave them unparented because I want them to stay in place independently of what the rig is doing. When I want the Targets to become inactive, I just keyframe them off. (Quick Tip: To deactivate a Target bone, with the Parent tool selected, Alt Click the targeting bone to select it then Ctrl Click an empty space. Then, when you wish to reactivate it the target or change to a different target, with the Parent tool selected, Alt Click the targeting bone to select it then Ctrl Click the Target bone.)
About the only time I parent Target bones directly to the rig is when I need a limb to follow the body's motion. For example, adding targets to the hip bones allows me to rest the character's hands on the hips while the character rocks side-to-side. (You can see this happening a lot in
my Puss-in-Boots demo.)
Hope this helps.