The official 'unofficial' answers in regard to touch trigger preparations are as thus (it has come up a few times, it may just be well buried within topics.
1) touch implies a living beings aura, yes. Metahuman, spirit, probably watchers...not sure about things like homunculi or spell aura's though (like magic fingers).
2) the alchemist is not excluded, meaning he can set it off as well.
3) this reflects partly to 2, but the preparation is basically armed right after the rolls are completed. So the moment the alchemy is finished, you got a live one right in front of you. It's strongly recommended you have something non living to grab it (like a robot or tongs) or put it in a very thick object to minimize aura contact.
4) see 3
This is one of those questions that people are hoping will get fine tuned during a bigger errata, because it does make live triggers very risky to handle. If things like magic fingers can handle it safely, then there is a few plausible options that are less of a problem, but until they invent Aura-sealing latex gloves, you want to give Fireball Preps a wide berth.