Hang in there! It sounds like you're doing great, having lots of patience. I think all kids go through this stage.
My son is 8, and has Aspergers/ADHD. With him, sometimes the questions are more of a nervous habit or a security thing. He will ask questions he already knows the answers to, repeat the same ones, check to see if I'm really listening, or sometimes he's pretending to be a teacher asking the class questions. He also constantly talks or sings. He walks around the house in the middle of talking to me, not realizing that I don't hear the rest of what he said(that's ADHD for you). One thing that sometimes gets him to stop talking for a couple of minutes is for him to listen to music with headphones. If the talking is driving me crazy I watch TV with the sound off, because I can listen and read at the same time, but I can't listen to 2 things at once.
When he's asking a question because of curiosity(for example what's the melting point of aluminum?), I can tell him That's a great question, let's write it down and look it up on the computer later. Or we can follow up by checking out a book from the library. I want him to keep that desire to learn, but not have to have everything he wants right this minute.