Scarlet Corsair is a fun class. Make sure to get an Arcane Stunt instead of the Grace +1 as a Swashbuckler, and consider more Rogue and less Swashbuckler, though if you don't care much about skill points, maybe stick with the current setup. I like Uncanny Dodge, so I'd try to get to Rogue 4 before doing Scarlet Corsair and top out with more Swashbuckler at the late levels, myself.
I happen to be building a fear-based martial PC myself right now, so I can recommend some things. I'm less familiar with Feint optimization. Feats to look for:
Combat Panache (PHB 2): Gives you a play dead ability, an Intimidate ability to cause the target to suffer your charisma mod as a penalty on his attacks, and an ability to make allies hit each other. The entire tactial feat is all about new uses for Intimidate and Bluff, your bread and butter skills.
Intimidating Strike (PHB 2): Standard action strike that if it hits, lets you roll to demoralize (as written, it does not restrict you to the target, if you can demoralize an area in a single action) as a free action. You can even take an attack penalty to gain an Intimidate bonus, but I'd rather just twink my Intimidate mod, rather than risk missing entirely. The main benefit is that the fear lasts the entire combat, instead of a hardly-worth-it one round. And you can take it at level 1.
Imperious Command (Drow of the Underdark): Despite the book it's from, the feat has no flavor or mechanical connection to the drow or the underdark. It's just a really, really good intimidate feat. When you demoralize an opponent from now on, he cowers for one round before becoming shaken, leaving enemies ripe for the picking.
Skill tricks are your friend, look in Complete Scoundrel. Never Outnumbered is awesome to do an area Intimidate (and can be used with Intimidating Strike for a multiround duration), though eventually Scourge of the Seas will make it obsolete. Group Fake-Out can tack on hefty penalties if feinting a lot of enemies at once, but can be combined with Corsair's Feint to deprive an entire group of enemies their dex to AC with a mere free action once/encounter.
For the late levels, while it would hurt your sneak attack and possibly cause brief multiclassing penalties (until you hit Warblade 2 and thus were Rogue 4 / Swash 3 / Warblade 2, with Rogue counting as favored class), look into Warblade. Or maybe Swordsage. Maneuvers from Tome of Battle can complement you well. In particular, I like the idea of a Corsair's Feint Group Fake-Out followed by Mithral Tornado or Adamantine Hurricane, to hit every foe around you and treat them as flatfooted (so you can sneak attack them). It's just stylish.
