Well, that all depends on what you mean by rigging the forearm.
In this example, I’ve rigged your arms in both FK (how you made them) and in IK (like the feet where if you move the foot the whole leg moves).
To use this arm set up, you should see a switch floating above each shoulder; one for each arm. Slide the circle in this switch to change modes. When the circle is at the top, the arms move as IK (when you move the hand the whole arm moves). When the circle is to the bottom of the switch, you can move the arms themselves. To make this easier, I’ve also made the arm controllers (the bones) hide themselves so you only see the ones needed for the current mode.
The reson you would want both IK and FK is that normally IK is used, but for movements like swinging the arms in big circles, FK can have better results. You should use the switch as either IK or FK… going half and half can be tempting but it makes for sluggish movement.
This set up is fairly complex (there are actually six arms involved and the switch takes a lot of setting up).
If by rigging the forearm you mean a smooth wrist twist, yes this can also be done, but I’m resting for the night now. I’m tired tonight… hope the above makes sense.
Glad you liked those feet
Main Character_Low_Poly_IKFKarms.blend (232 KB)