An attack is one thing and a campaign another, which is pretty much the WPRs stance; after a month or two of steady combat the distinction between a strike vs. de facto war is nominal and shrinking, so it should be the Senates call. Yet the Constitution does not explicitly require that, and DOES explicitly empower the POTUS as sole commander-in-chief, so whether the WPR is as legal as it is reasonable remains to be seen. It does have the advantage of clearly defined parameters though, whereas "urgency" or "imminence" are more subjective. I would not want to, say, miss the chance to get bin Laden because the opportunity was not considered urgent or the threat imminent enough to go without congressional notification and consent.

It may depend on whether he seeks a full joint resolution or just Senate approval (constitutionally, the latter would be more than adequate.) The Senate would probably go for it (though I know nothing that prevents a filibuster; Rand Paul will surely let us know ) but the House... well, perhaps the less said the better....

Not all, no, and it is hard get a head count in a civil war half a world distant, but it does look like a majority are Al Qaeda or affiliates.