1. Yes you can change the color of the button for ofline course only.
2. We need your ftp to make the phone number clickable.
3. Yes you can add the instagram icon. Refer : http://prntscr.com/jux286
@nursesed.net,
The Button fetch the theme Primary color. set the theme Primary color and your course button color will also change.
For icon: http://prntscr.com/jvbwrr