About the pain when using a mouse...My solution was simply making sure my chair was at the correct height so my arm is at a 90 degree angle. So my arm is resting on the arm rest and the wrist on the mouse table just under the mouse pad. That did the trick for me but it might not work for everyone.
That stopped my wrist pain not sure about hand pain. For hand pain the only thing I can think about, is getting a mouse that is the correct size for your hand. At least that's what I saw on TV from a so called expert on ergonomic computing.