UW version of Terminate, kinda. I think it's costed fairly, even though blue and white's removal should be weak, considering the existence of Vindicate and Maelstrom Pulse.

Well, the effect is very similar to Bant Charm, so yes, I think the cost is fine. The top-of-library option is very unlikely to get used since this is a sorcery.

Yeah, option 2 would get used probably about 90% of the time. Top is useful in some cases though, where you are removing their outs or maximizing your own by ensuring that they don't draw something specific, like let's say the last land they need to cast Cruel Ultimatum, or the actual Cruel itself, and so long as they don't draw those they can't win, even if they get to replay that guy you just bounced.

Another reason you'd use top is if you have something to mill them with. This would make sure that even if they manage to shuffle at some point, they won't redraw it.