I've since collected the various elements of the relevant material, because it was a bit spread out. Keep in mind that there's almost nothing anywhere in published materials regarding poisonmaking, and what there is is mostly shit.
1. Craft (Poison) follows the same rules as Craft (Alchemy) regarding materials: you pay 1/3 of the market price for materials, rather than having to seek out sources for poisons.
2. 4 ranks in Craft (Poisonmaking) prevents you from accidentally inflicting your poisons on yourself via the RAW percentage chance. At 4 ranks and every fourth rank thereafter in Craft (Poisonmaking), you add +1 to the DCs of your poisons. Craft (Alchemy) adds +1DC to relevant alchemical items in the same every-four-ranks progression.
3. Thrown weapons (encompassing alchemicals and poisons -- what have been previously described as splash/grenade-type weapons) can be taken as the subject of Weapon Focus and Improved Critical. Thrown weapons threaten on a 20, and a critical strike multiplies the DC of the thrown item by x1.3, rounded to the nearest whole number.
4. If you can sneak attack, you add +2 to the DC of a thrown weapon per sneak attack die when you successfully sneak attack with one.
5. Thrown weapons which do pure damage without a DC instead have x2 crit and add typed sneak attack damage when used in a successful sneak attack.
That said, as there are so few rules, there's probably room for other streamlining bits. Two things you'd probably want to consider would be vastly increasing the craft speed for poisons and possibly alchemicals, as well as increasing the amount of doses a character with skill points in Survival could potentially harvest from a wild source (I recall one memorable quote about RAW would require a character with a +30 Survival check to kill 14 purple worms for enough to make a single dose of poison, which sells for ~700gp). The typical solution I've heard is to create a feat called Brew Poison or some such equivalent to Scribe Scroll, allowing a character to make poisons at the rate of 1 day of crafting per 1,000gp base price, costing 1/2 cost of materials and 1/25th cost in XP.
Ofc. that's just in terms of the crafting side, and making it not insanely stupid. The sneak attack and crit applications are already pretty suited to it; a 1st level rogue would get to add +2 to the DC of their thrown items (or an additional 1d6 typed damage for something like a firestone) while sneak-attacking, while a 20th level rogue would add +20 to the DC/ +10d6 typed damage. The primary balancing factor here is that your main source of sneak attacks, flanking, doesn't work with ranged weapons, which means that you essentially either have to have excellent initiative and a backup for after you get your initial flatfooted attack, or take the Shadowdancer PrC for Hide in Plain Sight, or get a source of (preferably Greater) invisibility.