Does leukemia usually cause many symptoms?

Varies. Acute leukemias usually cause symptoms that bring a patient in to a doctor or emergency room. Chronic leukemias are often found incidentally when a blood count is ordered and abnormalities are identified.
Depend. Depends on type of leukemia. Acute leukemia vs. Chronic leukemia. In acute leukemia, symptoms will include fever, bleeding, fatigue, weakness, bony pain, chils, frequent infections etc- from supression of normal blood cells by the leukemic cells. In chronic leukemia- frequently presented with abnormal blood test without presence of significant symptoms.