They're all iffy, which is what makes it such a cool question. A real exercise in military, social, and economic history. They all sound decent, but when you get into the details, you realize how complicated the problem is.
Strategy 1: I'm torn on location. You need a culture that's has the capacity to take over the world (look at the ones that nearly did), but also one where a barrage of magical new ideas would be readily accepted. I'm thinking ancient Persia would be a great choice... but that's a tough call.
Strategy 2: My first thought is to find my way into Hitler's place and correct all the mistakes he made. Other possibilities include Napoleon or Stalin. In any case, there's not a lot of personal research you could do to adequately prepare for such an undertaking. How does one person, even with today's knowledge of the past, usurp one of the greatest empire builders of recent history?
Strategy 3: Yep, it's a stretch. What could somebody possibly bequeath via will or otherwise that could be wielded in such a way that I could take over the world? I can't think of a single thing, but it at least strikes me as a possibility.