For me, six was when my daughter started getting mouthy. She would sometimes say something mouthy before that, but 6 is when I had to stand back and wonder whether someone had replaced her with an angsty teenager.
I know this sounds counter-intuitive, but my thought at the time was that it was a sign she needed more connection with me, and not punishment. I started trying to pay more attention and be more focused when I was with her, like more fully present, and do more fun things together, and just snuggle more. We snuggle with little kids, but they get bigger and then we don't so much, and I felt like that is what my daughter was missing. That it was more about our relationship than her behavior - that the behavior was a symptom. I don't know if that feels like the same thing with your ds or not.
I don't know if it helped, to be honest, but she finally at 11 is really quite pleasant. We did have a long period of mouthiness, so she might have just outgrown it. I have been much better about really being with her when I'm with her - like spending time with her rather that sitting in the same room doing different things. I think it's helped our relationship anyway.
Oh, and I'd also ask her to say something over again. Like, "When you say that the way you did, it hurts my feelings. Can you think of another way to say it?"
I agree that they are not hanging on your word at that age and it takes a number of times asking sometimes to get their attention. I think sometimes a gentle touch on the shoulder can get their attention. Also, sometimes my daughter would hear me, and be planning to finish what she was doing and then do it, but she didn't tell me that. I told her and worked on getting her in the habit of actually responding and saying something like, "I'm just finishing this chapter and then I'll do it." Once she would respond and got in the habit of following through, I got less annoyed by that. I do know what you're talking about.
I have no idea about the low self-esteem thing. That isn't really a discipline issue, so I wonder if a new thread in just Parenting about helping a child with low self esteem might get some more input. You might want to start a thread there. My immediate thought is to keep trying different activities until he finds something he's good at, but I'm not sure if that's realistic or a reasonable way to handle that. I think you'll get some more replies here and I hope someone has some ideas for you.