OK, I'm a bit of a noob myself but I'll have a go at answering these to test my own understandings:
1) Steve Clarney was originally a Miskatonic Character but was misprinted as an Agency Character and has been left that way so that causes the faction number discrepency.
2) Partially correct. Pulled Under is a Steadfast card and therefore: From the Rulebook: "Steadfast... When a player drains a domain in order to pay the resource cost of playing a Steadfast card, he must have at least that many resources on the total number of domains he controls (and make a resource match as normal). So you at least need either 2 Cthulhu resources in one domain or one in each of two domains. The rest of it you have correct, ie costs nothing and you need to be able to exhaust a character with at least (T)(T).
Also from the FAQ: "(2.18) Steadfast: If a Steadfast card has a printed cost of zero, the player must still control at least a number of resources of the correct faction equal to the amount of steadfast necessary to play the card, although that player does not need to drain a domain in order to play the card."
3) Correct. Scotophobia removes the opponent's characters' printed Terror icons so they are now vulnerable to going insane (unless some other effect would prevent this).
4) I think I'm right in saying that Performance Artist would only disrupt the passive effect of Ghoul Taint once, ie you could sacrifice PA to allow a character with GT attached to commit to a story during your turn. In other words the PA doesn't get rid of the attachment, it only stops its passive effect from working for long enough to allow you to commit, then its passive effect kicks in again.