Great, so I can just use this one without having to upgrade into EV 8.0 SP5 then 9.0.4 R1 ?

as for the FSA file server agent, I can do that later on once the upgrade to 9.0.4 finished.

Yes, you do not need to go to EV 8 SP5. As you do upgrades you can refer to this TN:

Supported upgrade paths for Enterprise Vault (EV), Compliance Accelerator (CA), Discovery Accelerator (DA) and Discovery Collector (DC).

Yes, after you upgrade the server you can then upgrade the FSA Agent. 

Thanks Tony , so do I also need to apply this one as well ?

9.0.4_cumulative_hotfix_2.zip

You might want to.  Go through the ReadMe for it and it list the fixes that are contained.  You may see that it is worth while to go ahead and apply the patch if you think you could potentially be affected.

ah.. yes, because when I go to my Fileconnect, I don't see it there, but It was found from Googling around just in case there are fix to be implemented, then I'd implemented during the maintenance outage window (http://www.symantec.com/business/support/index?pag...).

So in this case when there is no issue affecting me since the upgrade time there is no way to test it out all stuff and features, then I can just skip it until the next Service Pack or even upgrade it to v10.0.3

yeah, the hotfix isn't on FileConnect but rather in a TN.  I would agree if you aren't affected to just skip and go to EV 10 sp3 when you are next able.