Thanks for the responses, everyone. And apologies for the time delay.
There seems to be a lot of divergent opinion on how optimal the various excellent feats are.
For the character, I'd like to have optimal damage (and conditions) output, even sacrificing damage at the risk of some defenses.
Though, perhaps oddly, I'm still planning on con 12 and cha 12.
He's largely an assassin / secret agent, so I'd like to maximize damage. The ranger feats would also let me finish out the skills I'd like for him to have. Simply put, I think he needs a total of 8 trained skills to be the sort of secret agent I'd like for him to be.
That being said, I'd willing to reduce some of his skills (perhaps he's just not trained in, for instance, perception, just yet) to up overall damage per encounter, or to maximize the chance of a truly damaging first strike.
This is why I was looking at the ranger feat: Additional damage that can be directed at a particular foe, making it possible to do even more damage. This also lets me pick up all the skills I want. A win-win.
The character is going to be human, so there are also the human feats. As great as Action Surge is, since sneak attack only happens once a round, I'm not sure if this is as useful as it is for other classes.
As for weapon selection, I was thinking the dagger. It can seemingly be hidden better than a rapier, and its easy to carry quite a few of them.
As for the other feats, here's why I want each:
Improved Initiative: First Strike. A rogue going before the target he has decided to take out is a huge deal.
Nimble Blade: I had forgotten about this one when I first posted. Another +1 to attack roles seems good ... but could it be overkill? At first level, without NB, he's got +8 to-hit with daggers. If the average AC is 15, he only need a 7. There seems to be diminishing rewards with the to-hot bonus continuing to increase.
BackStabber: Damage++ 2d8 feels, in the hand, a lot heftier than 2d6.
Weapon Focus: Damage increase FTW.
Two-Weapon Fighting: If I go with two daggers, this is another way to increase damage. It could be either that or keep the hand free for potions, which seems unnecessary.
Two-Weapon Defense: As I'm planning to stick around in melee, increasing AC a bit might be worthwhile.
Quick Draw: I do like the notion of there not being an action to draw potions and daggers. The initiative bonus is also nice. Does it stack with Improved Initiative, or are they both feat bonuses?
I hadn't given much thought to Weapon Proficiency. Are the weapons in the Adventurer's Vault better for the rogue than the simple dagger?
Skill Focus is another interesting idea, as I do plan for him to be fairly sealthy.
Other multiclass feat: I don't know. I like the ranger one as it increases damage done to a specific enemy. It could make me a striker on steroids, which would be great. The fighter one seems overly limited: +1 on one attack doesn't do it for me.
Those are my thoughts. Am I crazy, half-baked, or does this seem not far from pretty decent?