Does rhabdomyolysis usually cause many symptoms?

Depends. On the severity of the rhabdomyosis; one may have minimal symptoms to having diffuse muscle pain/weakness. In very severe cases, it could lead to renal failure and can require dialysis.
Yes. Pain in the muscle that has been injured is expected, and patients can have abnormal urine color and flow because injured muscle tissue is trying to be excreted in the urine. At its worse, the kidneys can shut down all together.