SRD said:
If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon...The same rules apply when you throw a weapon from each hand
The rules say nothing about the type of action you must take to get the extra off-hand attack(s). It is just as applicable if you are using a flurry of blows as when you are getting iterative attacks with a regular weapon. That having been said, here's the full breakdown, as I understand it:
Flurry(must use shuriken) +5/+5/+5/+0
extra off-hand attacks(can be any thrown weapon) +5/+0
Rapid shot (any thrown weapon, technically part of the off-hand attack) +5
Haste(any thrown weapon) +5
Just a comment on this situation, some people are like "8 attacks at lvl 13!!! that's so broken", but if you look at it, it's 6 attacks at -4 from base, and 2 more at -9, also the majority of the attacks (3 primary plus one secondary) are 1d2 damage with no str bonus added
I was incorrect previously, shuriken can be drawn as a free action with no feat, note they also are at 1/50 cost to enchant, but can only be used once. Tanglefoot bags, on the other hand, are regular thrown weapons, and must be drawn as a move action (or part of a move action).
(house rule-ish) You could have a few tanglefoot bags in one hand, and use the other hand for all the throwing, which lets you throw a limited number of tanglefoot bags without having to spend an action drawing them.
I can't find any official rules on poisoning, but it seems that is the only potential problem with this concept. What kind of action is it to apply poison to a piece of ammunition? How long does the poison remain effective once applied?