Just bumping this for you as I don't know the full answer, but,
1. The only private candidate I have known personally, got their private tutor to provide a predicted grade, then school spoke to private tutor to make sure tests and mocks for the subject were done under controlled conditions. They were satisfied with the prediction and it went into the UCAS form. The student achieved the predicted grade.
2 - You're supposed to write your own Personal statement (loads of guidance and sample you can look at on TSR) unless you mean someone to read it before you submit? could you approach any of your old teachers?