Also to answer question one, in Detox from Season 1 at the end when House admits to being an addict, Wilson talks about how much he changed, and he said that the change wasn't because of the pain after the infarction, but because of the pills.

So it dosn't exactly help with where Wilson was during the infarction but it definitely proves that Wilson knew House very well from before it happened, which fits in with the Birthmarks timeline, and I would asssume he was around during the infarction and aftermath. I wish they told us more though.