You definitely were not "very clear" at all. I did read your original post, and what little information it contained posed a risk to you of deportation and fines. That's why I responded.
Next time be more clear. Oh, and 70 + 60 is 130, not 140.
Heck, who knows whether immigration will be kind to you or not on your proposed second visit? To them, if you return very shortly after a stay like 70 days, they might think you are up to something. Like Wonko wrote, Japan is not a country to fool around with when it comes to immigration matters, no matter how innocent your motives are.
And there is still no "tourist visa" for Americans, black or otherwise.
To answer a couple of your questions directly, though, instead of just giving you some sound advice before you plan anything...
1. Mid-August is Obon season, when ticket prices and accommodation prices run very high.
2. Without a real visa, you will need to show the airline, not immigration or customs, that you have a planned/paid exit, whether to return to the States or go elsewhere.
3. Yes, that includes to Korea.