I’ve been playing a character with Alchemy and Enchanting for over a year now. The answers to these sort-of depend on your groups play style / interpretation of the rules but here’s how we’d handle these cases:
Using Alchemy/Taxidermy on a corpse is only one of many possible ways you could figure out a creatures traits. If the creature is particularly common you may not need to test, or you might be able to use a wise… or any other method you have for gaining information. So depending on the situation you might not need to test these particular skills twice. For example my general process was: “I need a particular trait for this” -> Wise / research test to know where to find a creature with that trait. If you’ve ended up with the corpse of a creature with unknown traits that’s when I’d use Alchemy / Taxidermy for identification.
I don’t think the rules say anything about this so I guess it depends on your setting. Remember you can use Intent and Task to do pretty much anything within reason, and when it comes to magic the definition of “reasonable” is pretty broad.
Yes. You’d need a suitable source of relevant information to fuel your research though.
There is no list. You basically have to make a ruling here about how Alchemy should work. Generally we’ve just used Intent and Task: “I want to make a potion that does X” and set the Ob based on the potency of the effect, possibling throwning in some extra challenges (finding rare ingredients) if it’s a big ask. If a character has Enchanting and Alchemy its probably a bit cleaner rules-wise to use Enchanting when its subsystem’s rules cover the effect you’re going for. EG A potion of water breathing could be implemented as a one-shot trait transferance enchantment instead.