do i set up IK in the spine

[lstaples]

if so do i go from the root to the neck or head
also while painting weights and i bend the leg for instance and paint while its bent
how do i get back to the posed position and with the handles in the right place
also do i want to constrain the joints somehow so the model doesnt colapse in weird ways or just bend unrealistically

[Professor Watkins]

I usually don't IK the spine. If you do, it's probably best to use Spine IK to do so. My personal preference is to not IK the spine, and use FK for animation of the upper body.

You need to return to the bind pose. This means that you need to return the IK handle to the exact same place it started. To make things easiest, before you move the group that is the IK handles, Freeze Transformations which will make its X,Y,Z position values 0,0,0. So then you can quickly enter 0,0,0 in the Channels box to get back into position.

I would not do any constraints for the joints. If you are using FK for the upper body, usually the animator will be grabbing the exact axis he needs when animating; so no need for restricted movement. For the lower body, if your IK is set up right, usually there is no need to adjust the range of motion; and in fact doing so can bring upon undesired results as it restricts the solutions Maya can use to rotate the bones into positiion to aim at the IK handles.