"Laws" are not derived from "case law" - DECISIONS are derived from case law.

Common law can either be case law that interprets legislative statutes, or it can be case law that is only based on principles from prior case law.

Case law refers to common law. It is a law that is made by judges through the decision of the court.

Case law should be used as a means of interpreting statutory law. Statutory law is held higher than case law. Case law can be overturned in the process of interpreting and applying statutory law, but statutory law cannot be overturned, only amended. If analyzing law, see statutes first, and apply case law second as a means of defining the statute.

No. "Case law," also called precedent, controls a case only if it has not been superseded by statute. The only exception is case law regarding the constitution.