Thanks for the reply. No worries about that. In the meantime, I was trying to resolve these issues myself and came to the following conclusions.
Re 1: You can fix this issue by adding a custom CSS class to the stack with w z-index included. Nonetheless, it would be great to have that fixed at some point.
Re 2: This is still an ongoing issue. The cover feature and full-screen slider lack compatibility in the mobile viewports, however, the rest of the issue can be resolved by adding the z-index in the custom CSS.
Re 3: This bug is still there, but, now I understand better what is causing it. If you place and centre video embed (i.e. Vimeo) in the mobile viewport with “Use Browser Height for Row Height” option and cover feature active, and then add another element such as text (like I did “Project information“ in the screenshot above) to the same row, the whole layout will go out of the window. If you remove the text element or place it in the stack together with the video embed, the site is coming back to normal.
Nothing new regarding 4 & 5