Questions regarding keyboard-guidelines

Hello,
   
   
  Unfortunately, I have problems understanding the guidelines "2.1.1  
Keyboard" and "2.4.3 Focus Order". 
   
  My specific questions would be:
   
  -Which elements should  be focusable - only interactive elements or  
also non-interactive content such as text? (There is contradictory  
information about this on the Internet)
   
  -Do the guidelines imply that the user must be able to only use the  
tab key to access all focussed elements on a screen? Or would the  
arrow keys or a combination of tab and arrow keys also be permitted?  
Are there any rules on how such a combination of tab and arrow keys  
should be implemented?
   
   
  An answer to my questions would be incredibly helpful.
   

Thank you in advance for your feedback.