I downloaded the latest release branch for 4.8 and did not see very many of the issues you reported.
I was able to use the Minimize button in the main viewport to minimize the program.
I was able to use Ctrl+C / Ctrl+V to copy/paste as well as use Ctrl+W to duplicate inside the material editor.
I could also drag from a pin on one node to create a new node.
The “X” to clear the content browser search bar was working for me as well.
I did experience a hang while trying to save a material if I was in the process of compiling shaders. This is actually expected behavior since saving while compiling shaders is not possible anymore. The hang ended once the compiling process finished. I did not have any issue saving at any other point.
In what way was the Fullscreen mode freaking out? I used F11 to make the viewport fullscreen but did not experience any issues.
The issue with projects saved outside the default folder location not showing up in the project browser has also been reported (UE-17253).
Thank you for letting us know about the issues you’ve come across so that we can work on fixing them however please keep in mind that it is best to post issues separately to make it easier when searching for a specific issue.