W.r.t. your questions:
1) Strength is helpful if you are going to carry armor / loot / stuff. Yes, I'd prefer Con.
2) Many monsters lack sense motive. Against those, you might have a decent chance of getting a feint to work. I favor Combat Reflexes + Versatile Flanker + Adaptable Flanker + Reach + Penetrating Strike ACF to make sure SA really hits.
3) Double hit is puzzling without combat reflexes.

Wraithstrike is very good for melee, but it's coming online quite late in this build. Swashbuckler is also doing relatively little for you---I don't see the point. You're BAB is very low at the end (+11).

Is the concept a smart/sneaky fighter? Or is spellcasting a part of the concept? An alternative build is something like:

Rogue 3/Wizard 2/Unseen Seer 10/Arcane Trickster 5
1. Two Weapon Fighting //I'm assuming this is what you want.
Human. Combat Reflexes // Prereq, but also good in combination with reach.
3. Vexing Flanker //prereq, but also gives +2 to hit.
Rogue 3: Penetrating Strike ACF //SA the SA immune
//Buy Feycraft weapons instead of using Weapon Finesse
6. Practice Spellcaster[Wizard] //caster level+4
//Buy Rods of Silent Spell instead of taking Silent Spell
Unseen Seer 2: Pick up Hunter's Eye for +level/3 d6 SA damage
9. Adpatable Flanker //You can flank for yourself if you have enough reach.
12. Arcane Disciple[Competition] //gives access to Divine Power (BAB=HD) and Righteous Might (+1 size which gives you more reach)
15. Arcane Strike //+spell level to hit and +spell level d4 to damage for 1 round.
18. Craven? //+level SA damage. Could use Improved Two-Weapon Fighting instead.