Wow, reading fail on my part. Sorry!
Anyway, as it seems like you'll need to hit twice with your arrow to get the full effect, you may want to consider the Slow Time shout to make that more likely - especially if you're facing melee types who just want to hit your face.
Alternatively, see if you can get any slow/paralysis effects in tandem with your Weakness to Poison poison; that'll help you get more time.
All 3 words of Slow Time (augmented by the Stability perk in Alteration if you feel it's necessary), plus a Quick Drawn longbow (or maybe Zephyr if you want to deal more damage - not sure which is faster), plus a suite of poisons (created with Fortify Alchemy enchantments), plus the Augment Fire/Frost/Shock perks, plus Ahzidal's Mask, plus Fortify Destruction potions would be *extremely* cool to pull off. You'd need something like this for a perk setup:
Destruction: Novice-Master, Dualcasting, Augmented Flames (2/2), Augmented Frost (2/2), Augmented Shock (2/2), Intense Flames, Deep Freeze, Disintegrate
Archery: Overdraw (1/5), Eagle Eye, Steady Hand (1/2), Power Shot, Quick Shot, Critical Shot, Hunter's Discipline, Ranger
Alteration: Novice-Expert, Stability, Resist Magic (3/3)
Alchemy: Alchemist (5/5), Physician, Benefactor, Poisoner, Concentrated Poison (this is of questionable use... I guess you'd save it for when facing multiple opponents, since it would be wasted against single-foe fights)
Enchanting: Enchanter (5/5), Corpus Enchanter, Insightful Enchanter
The Destro perks assume you're not specializing in any element, and also assume you're working toward the Master spells. Impact isn't needed, thanks to Slow Time and other CC effects (poisons of slow/paralysis and Power Shot).
Only 1 perk in Overdraw, since we're not trying to kill stuff with the arrows. The right side of the tree might not be strictly necessary, but Ranger is a fun addition, and allows you to keep distance in order to make that second shot.
It might be considered overkill to perk out Alteration just for Stability, but on the other hand Magic Resist is a great passive effect. I don't think it's necessary to grab Mass Paralysis, but you could argue that, since you're grabbing Stability anyway, it's not too far out of your way.... You might also want to pick up the Mage Armor perks, if you're feeling squishy.
I'm still debating Concentrated Poison... on one hand, it would have great utility against masses of foes, allowing you to apply poisons twice as fast. On the other hand, it'll hinder you in 1-vs-1 fights, since you'll *have* to shoot 3 times in order to apply both poisons (2 shots will be Weakness to Poison, and your 3rd would be Weakness to X). I guess for those single fights you could just live with a single poison effect?
Enchanting might not be necessary, really; it's just to amp up your potions/poisons. I guess it depends on difficulty and how OP you want to be.
You could also work on Sneak as an alternative way to get poisons in before a fight begins. Problem there is, why not just become a sneak archer?