RE: Minimum Power to Weight?
what are you classifying as power ? what units ?
maybe thrust to weight ? ie 1.5:1 would give you a decent pull out from a hover ?
but how do you measure thrust of an engine/prop combination without building a proper thrust rig.
Maybe a better answer is enough thrust to pull out of a hover with plenty of authority, this will also be enough for other 3D stuff like waterfalls.