I Want To Optimized A Human Rogue/Swashbuckler

[Bartmanhomer]

A must-have for any Rogue/Swashbuckler is the Daring Outlaw feat. That makes Swashbuckler levels advance your Sneak Attack dice, letting you get the best part of being a Rogue on Swashbuckler's better chassis.

I don't think you can take that until 9th level, though, so for your 6th level feat you probably want either Improved Two-Weapon Fighting or Staggering Strike, for increasing your number of attacks or making each one a deadly threat respectively. There's also a magic item that will just give you Improved TWF if you already have TWF (the Glove of the Balanced Hand, I think? Something like that), so see if you can get your hands on that... no pun intended.

I'd suggest taking the penetrating strike ACF from the Lightbringer Rogue so that you can still get some sneak attack in against the otherwise immune (and apply craven to them).

Swapping things around so your advancement is Rogue 3/Swashbuckler 2/Rogue 1/Swashbuckler n unambiguously allows you to take Daring Outlaw at level 6.

Well as Bat-Mite say: Oh wow, awesome sauce.