Preliminary thoughts ...
Sleeping Tiger (UA) Monk 2
1ACF: - Weapon Finesse, +2 Hide
2ACF: -Evasion, Bonus Feat; Invisible Fist, Improved Initiative
Rogue 3
3ACF: -Trap Sense; Penetrating Strike
Assassin 7 or Assassin 5 Swordsage 2
For working with poisons ... Master of Poisons (DotU), Deep Poisoning (DR# 322) ... Sickening Strike (DotU) ... Terrifying Strike (DotU)
... Aleval School (DotU).
Atramen Oil for further reducing fort saves (Planar Handbook); malefics from dragon 301 to enhance poisons (some even seem plant-based if you can mix in minor creation by some item).
Daggers are cool and you could have an invisible blade with them but they work fine for just about anyone, though if you go into swordsage might not quite measure up to shortswords in melee if you're not invisible blade / daggerspell mage / so forth. Still handy.