1-Technically you can do everything with CE. But the question is how easy;
In my point of view Pentaho EE has 3 killer tool that CE hasn't
Dashboard Designer,
Interctive Reports,
Analyzer
Without these tools you may need somewhat programmer skills like as JQuery, XML, Javascript , CSS , maybe xAction ...
Also you may have difficulty to provide some functionalities that business users claims.
You can check full EE-CE comparision from here: https://partners.pentaho.com/wp-content/uploads/Pentaho-CE-vs-EE-Comparison.pdf
Moreover, Pentaho CE documentation a bit problematic ( Some topics refers to EE not CE)
2-No limitation
3- Yes . In that case no difference between CE EE