Q5: Does this mean that CentOS Stream is the RHEL BETA test platform now?
A: No. CentOS Stream will be getting fixes and features ahead of RHEL. Generally speaking, we expect CentOS Stream to have fewer bugs and more runtime features than RHEL until those packages make it into the RHEL release.
In other words, this new operating system called "CentOS Stream" will be getting new software features and new attempted bug fixes that aren't yet in the official "RHEL" release. That's how a beta release works.
For the curious: RHEL is Red Hat™ Enterprise Linux, intended to be a stable platform which industries can rely on being solid and reliable for a guaranteed number of years. CentOS is/was a free version of these produced by a consortium of Linux users including CERN, that lacks RedHat support. IBM bought RedHat, and appears to have leaned on the CentOS consortium to change their model.