I'm guessing that while Briggs was totally high on drugs he told Jangles about the first House. As soon as he got out and sober he remembered what he had done, called the house and then his girlfriend to warn them but it was already too late. And being a sadistic psychopath Jangles let him live so he'd feel guilty for the rest of his life.
Also it was kinda obvious that the Federale was the real Jangles, even without the gunshot wound. Whatevs.
And about Juan/the "undercover approach": I don't think he wanted to frame Briggs. He just wanted to confront him to hear the truth, and since Mike told him that he was done with the investigation this was the only way for him to do it. In his dispair to find someone to blame (apparently he hasn't reached the last stage of grief, accaptance, just yet) Juan played dress-up and got himself shot (at). These agents are all totally messed up! xD
Yup, I was right. Briggs is doing all this for a woman. Jangles killed her so now Briggs is on this crazy one man mission to destroy the Cartel and kill Jangles. They did seem to fill in a lot of pieces this episode which is nice. Though I think they were a bit too liberal... SEE THIS GUY HE"S JANGLES!!! And in case you did not figure it out from the suit and gun LOOK BULLET HOLE FROM WHEN MIKE SHOT HIM!!! Granted when he was introduced I was pretty sure he was Jangles anywho, but they could have left us in the dark about it a bit longer I think. Though I wouldn't be surprised if Jangles was one of the people from the Estate. I pretty much suspect it was Briggs' TO.
I actually think Paige is pretty fleshed out. She is incredibly loyal. The real question is if she is badge first or house first. There have been several great scenes where Paige goes from bubbly happy go lucky fun time girl to serious DEA because that's her job. It also feels like the writers want to push a Mike + Paige story which is too bad because I really liked Abby. In a show about lying it was interesting to see how the lies are different between the agents in the house, for a cover and aim at civs looking in.
Good to know Juan was pretty much just crazy. Getting all artsy critic the parallels between Juan and Briggs are interesting. They are both after who they think are responsible for the Estate and it really seems like they are both willing to burn everything to get their "justice" ... So the question is will this show end with Mike shooting Briggs like Briggs shooting Juan.