Re: Joker Knew of Bane's Existence.
Yeah, Joker is proven right in the end, but no way he was expecting 8 years to pass before the truth about Dent came out. The Joker accurately predicted most people's actions in TDK, but two major ones he didn't were the ferries choosing to not kill each other and the Batman taking the fall for Harvey. He was expecting the truth about Dent to come out imminently, but with the noble lie Batman is able to prevent the Joker from winning.
We have no way of knowing whether Joker had heard of a new LOS plot or Bane (I'd guess not) but even if he did, that has nothing to do with his own plan for Harvey.
The idea that The Joker decides to take action because he knows Gotham is doomed anyway and sees it as a big gag is an interesting notion, but I prefer to think of him as a force of nature all his own and that's definitely how TDK portrays him.