First I don’t know if you’ve done the BSOD Character Animation Tutorial, if not, take a look at it at least from the rigging point on. There’s also another advanced rigging tutorial in the BSOD section that explains IK and other constraints (both links in my signature).
There are links to some great rigged characters in my “Best of Blender” thread in my signature, that you can use or study.
Second, when using IK constraints, you almost never want to leave the ChainLen parameter at 0. Legs and arms are typically set to 2. Your neck IK should be 1. I wouldn’t use an IK control for the head or neck, but that’s your preference. I find it hard to animate IK head / necks, but I’m just a beginner at animating.
The Limit X/Y/Z rotations are also doing weird things with the leg IK constraints. I turned them off and the legs work properly. Personally I wouldn’d bother with the limits, if you want to make them work, perhaps someone else can explain how to make them work.
I also suggest either turn on the Hinge button for the foot bones or (preferably) add copy rotation constraints to them targeting the IK foot targets, and rotate the IK foot targets in EDIT mode to match the starting positions of the foot bones), so that when you move the pelvis down the feet stay flat.
You probably don’t need 5 handbones in each hand either, just use one and make all the finger “X-1” bones children of the hand bone. You could also make the fingers IK chains (without targets / chainlen 3) if you want or study the Ludwig / Mancandy rigs for more elaborate finger controls. Both those rigs have great facial setups too, as does the A.J. rig.