Mr. Barr is required only to provide lawmakers with very basic facts. He would be operating within the guidelines of the regulation if he were to give Congress a bare-bones notification that Mr. Mueller had concluded his work.
Will the Mueller Report Be Made Public? Answers to 6 Key Questions
28 CFR § 600.8 - Notification and reports by the Special Counsel.
Wrong.
See above post.
Your link says "can and should" release.
The law (as I posted the link) says "AG doesn't have to release"