(3) Adjusting the width of columns cannot be preserved. (2) You can't change the viewing screen e.g. To open the PDF, you would have to open another window or with another program (Adobe Acrobat). (1) You can't preview PDFs or full-text on the main window's sidebar anymore.
I would recommend keeping the X9 version, as EndNote 20 has revamped their UI and is missing a number of key features. They removed the download link to the X9 version and now offer the new EndNote 20.
You can find the download links here (requires login) RMIT has updated their software hyperlink this year.