The Joker Blogs/WMG

Harley will break the Joker out of police headquarters.
Harley, in a state of turmoil after the murder of her fiance, will set out to rescue "the only thing she has left to hold on to." At some point in the next season, they'll escape together.
 * "Say hello to your new and improved Harley Quinn!"

Ted the Bum gets the joke...
Which is that The Joker has given his life meaning again by turning him into a killer. He also suddenly realises that they're now the good guys because they're dressed up in a cop car. The whole joke is that whether you're sane or insane all depends on where you're sitting.

This Joker DOES want Harleen Quinzel
Oh sure, he's using her like hell, seeing that there's something there he can use, but when he finds out she's moving away to Metropolis with her fiance, he quickly finds a way to stop her, and incorporates stopping her leaving into his big plan to get Arkham sold to the corrupt Lex Luthor. Getting Arkham sold to Luthor (thus having Luthor in his debt, and being able to stay in Arkham, where he wants to be) was the big plan but there does seem to be some sort of twisted desire for Harley there - all he really needed to do was threaten Jeramiah and get rid of Lyle (he doubtless could have worked with any new therapist to get them on his side too), but he killed the best man to take his place, and showed up at the wedding too, all in that tux. There was almost certainly a part of him that wanted to keep Harleen for himself - and he got to do just that.

Ted the Bum is Chester A. Bum.
They dress exactly the same, Chester lives in Chicago, and The Dark Knight Trilogy's Gotham is Chicago. Most obvious reasoning: They're Alternate Universe versions of each other.

The "secret" that Jim Gordon has stashed in Arkham, alluded to in Further Evidence #2, is...
Harvey Dent. It's a well-known WMG that Dent survived his fall and was quietly tucked away in Arkham.