Default Questions on Flashing Omnia II ROM

Hi Everyone,
I am trying to flash the rom on my Omnia II for the first time so I need some advice. My device has following versions:
PDA: I8000NXXIJ9
CSC: I8000XSOIJ2
PHONE: I8000DXIJ1
I wanna update the JD3 rom but I have few questions,
1) Is it possible to update only PDA and CSC part with JD3 or any other rom leaving eBoot and PHONE part unchanged? Or combination of 3 leaving either eBoot or PHONE part unchanged. Is there any benefit of updating eBoot and/or PHONE part?
2) I am also confused with PDA part. There are upto four parts (files) of PDA to download. My question is, do we need all of them? Or just need part one? And I think we can only select one file on the Octans downloader window.
Can anyone kindly clear my concerns and help me in this regard.
I thank you very much in advance for your response. Any reply would be highly appreciated.