How do I fill the PBN\ part in a Flight Plan Form?
You have 8 items selected, and the max allowed is 8. There is guidance material from ICAO with steps to follow on how to get down to the 8 (in case you exceed it in the future). Right now you're fine.

For example:


  If having applied the guidance provided in Step 3 there are still more than 8 PBN codes remaining:
  
  
    
    Identify the capabilities considered to be the least relevant to the flight;
    Insert them under Item 18 within the NAV/ element;
    Insert the letter 'Z' in Item 10a.
    
  
  
  For example, the codes relating to long range Oceanic capabilities (A1, L1) will not be a priority if the flight will take place entirely within European continental airspace. Inclusion of an RNP APCH capability will not be a priority if none of the destination or alternate aerodromes provide such a procedure.