I got super busy at work so I haven't gotten a chance to read everything but some stuff I didn't know prior:
They planned on killing Kima on episode 10. Originally she was going to die
After Omar and Brother Mouzzone killed Stringer, they were going to piss on him. Idris Elba told them if they did that, he was walking off set, so they didn't go along with it. Ed Burns says David Simon should've never let Idris talk them out of doing it, but I disagree. It would've ruined it for me. Idris was upset about his character being killed, so the pissing just added insult.
None of the actors ever know what's going to happen ahead of time. Actors don't even know their character is dying or even what the next storyline is until they get to that script for the day. Some kinda figured it out before they were told, like Bodie knew early in season 4 his character was going to get killed, just using context clues.
I did know this part already but Season 3 was written as a Series Finale, because everyone assumed the show was done for good. They had to get fans petitions and meetings with HBO execs to get the final two seasons to finish out their story, but the show was all but done after season 3.
After Season 3, when they didn't think they would get renewed, they were going to do a spin off called "The Hall" which was going to be 75% politics (Carcetti, Royce, etc...) and about 25% of the street shyt.
Neither Ed Burns or J.D. Williams thought Bodie should've showed any hesitation in killing Wallace. Prior to that scene, Bodie was seen as a hardcore/no feelings character, so they didn't believe it fit with how his character was portrayed up to that point.
Another thing I know but I forgot, but the actor who plays Lester Freamon was originally going to play the role of Stringer Bell
The actor who plays Chris Partlow was going to be Slim Charles but he turned down the role, and then later got recasted
The actor who plays Slim Charles auditioned to play Marlo
Michael was originally casted to play Randy's role and Daquan was going to be Michael
They had to basically bribe Dominic West to return after season 3. He wanted to go back home because he missed his daughter, so they lessened his role in Season 4, and allowed him to spend more time with his family, but they let him know they needed him for Season 5, because it was gonna be built around him.
Despite popular belief, no character on the Wire is based off one person. Every character is based on multiple real life people. For example, Avon is a composite of like 5 different people. Same with even Ziggy.
I'll be back with some more
Lance Reddikk and Dominic West didn't get along too much because Dominic was sort of a funny man during scenes, trying to get people to break character, and Lance didn't appreciate it.