Wide range. Zero to "very high" (eg 100's of thousands). Leukemia undergoing treatment may result in a zero white blood cell (WBC) count. Some leukemias may have relatively normal total WBC but abnormal cells (blasts) in the differential. Other leukemias can develop very high WBC counts. So, a wide range is possible.
It varies... It varies widely and it's not always dependent on the type of leukemia. Usually, the WBC count is elevated but it can also be normal or even decreased. Some types may be associated with very high WBC at presentation (in the hundreds of thousands), like cml, cll, t-all, but it's difficult to give you exact numbers.