These are ten year old kids. I'm sure the interviewer will know when a child has been coached with interview answers.
My dd went to two indie interviews, never did any of the above suggestions and got offered both places.
I think it's important to be yourself. Interviewers will be experienced in drawing the best out of a child. By all means encourage a child to chat when spoken to, but I personally would not advocate going so over the top.
I'm with SnowDrops. Trying to get my stubborn DS to do any of the above is a hmmm type of moment. He's 10! Perhaps that's a problem and he will fail though. Only time will tell. Each to their own, though, and if it works for you guys, great. Us, much more low key just a reminder to do eye contact and be polite (which most of the DCs going for these schools will be in any case as a matter of course, I'd have thought) ..... Good luck to all.