I like the plans, I just want to know if we actually have these poisons. I figure if we could set up an alchemy lab in the back of the wagon (It's probably still there from when you bought it unless it fits in a haversack) Then we could either stop for a couple hours for you to make the poison, or you could take some small penalty for making poison while we're riding down the road.
I just recommend dispatching the supply convoy first before killing anyone to ensure that the convoy is being guarded and run by bandits and not hapless merchants who have been bullied and threatened. The part where we actually keep around the captured bandits is a different matter. From a moral standpoint, wiping out the bandits is good, whether we should kill them, knock them out and destroy their weapons, base of operations, and supplies to prevent them from amassing such a scourge again, or knocking them out, tying them up, and bringing them to jail is an ethical dilemma.
I mean Dharsus, being Lawful good now would probably recommend sending them to jail, because killing them would set their souls free from atonement and on the cycle of reincarnation (I copied some belief system that justified ninjas in killing people because of reincarnation so they wouldn't all be evil, it's probably not cosmologically true in the campaign setting) We can argue about the ethics and morals of killing killers in character and decide what to do with them.
As a rule of thumb, if we let them know that we're here to pay them back for their crimes and not just another bandit band closing in on their turf, then we can be justified in using unrestrained deadly force when most of them respond by trying to kill us. We can make heal checks to save the unconscious after people have stopped swinging swords at our heads.