I know not of this FAQ redpandamage spoke of. So I'll just answer from what i know
I mean honestly I can never find faq's peopel talk about anyway.
In general most of the info is in the core book, some in the new alchemiy manuel i think as well. Generally a lot has never had an update after core (see poisoner's jackets which are very sad because they refer ONLY to core book poisons)
1) no no real rules on this. So really RAW would allow them to keep for years. Thats how various super ancient traps in dungeons still have valid poison. It's not like someone is going down every hour to repoison it. Kind of a mean and weird homerule considering the cost of poisons and all. I could see it being washed away (though most of the poisons describe ichors which wouldn't) In general I think its much better for them to last as long as possible. Just from all the issues with making and using poisons.
Poisoning sheath isn't the best example for time duration. It's used for players who have no ability to resist poison to use it. It's meant to allow players to try and poison their weapon without poisoning them. and to "save" that one dose for when they need it in a fight.
i.e. its better to poison yourself before the actual fight than to take the long and risky actions in battle to pull out, and poison a weapon(possibly poisoning yourself)
instead, using the item you put the poison in it (if you poison yourslef. big deal your in a safe place). THen you can use your sword all you want until you get to the target. Then you sheat and unsheath yourweapon and stab him with your poison.
The game already includes many MANY ancient non magical traps that still have active poisoning. It's really only specific magical items to help that make non lasting poisons. (the sheath degrades it in it's use. Poison jacket/greater and lesser, makes temporrary fake poisons as well so they degrade (its really so they don't sell it)
2) the inhaled and injested stack straight up. The rules being (for those two)
Increased Duration: Increase the duration of the poison by 1/2 the amount listed in its frequency entry.
Increased DC: Increase the poison's DC by +2.
So lets take a poison.. Ungol Dust. Inhaled, DC 15 onset null, frequency 1 rond for 4 rounds.
So if i stacked together in a drink, 5 doses. The DC would then be (4x2=8+15)23. The frequency would be increased by 1/2(four times) the duration. (one half of four rounds is 2 rounds. that occurs 4 times) So the new poison is this
UngolDust (combined into one dose mind you) onset null, frequency of once a round for `12 rounds (for the listed damage each time a fail occurs).
This is why (the so very few ) people who use poisons will stack alter a cheap decent poison like Drow Poison (injury) into inhaled, so they can stack them up into being useful. Usually on an alchemist version. Because the costs of high level poisons is too much to really use.
There is some room though (its a gray ish area) as to whether combined inhaled doses are now "one dose" or just a bunch doses. But if your gm rules they were one dose. you could convert poisons to inhaled make a super poison then convert to a injury, and use the alchemist 6th level talent to slash the hell out of people.
3) Isn't really covered in any sorta ruling that i know of (try to find that FAQ) but most GM's will treat inhaled poison as they would smoke or clouds. Which there are rules for already in the book. So if the faq doesn't cover it treat it like that. (also makes them more effective which is good considering the costs. and I'm ok with that as a player even if used agianst me)
4) Uh. I don't know the trap crafting rules. THey already exist though so you'd have to look them up. But baring any extra special rules, then traps are like any other poison applications. Single for injury/contact. multple for ingested or inhaled.
5) not a clue. Again you'd have to look up all the trap rules.. You could probably find them easier on d20pfrsd than digging through each book. They are pretty good about updating various things quickly.
