I'd say, don't bring in Sly McCoy.
It was nice for the fans to see him regenerate (even if he went out rather shabbily), but useless for getting any new viewers interested.
Sly himself says it was a mistake (adding that he didn't regret it because 'the money was very good', obviously with a smile as he said it) and they should have let the new Doctor stand on his own two feet first, and then maybe later done the transition in flashback.
Speaking about the new series, Russel T Davies said that if he had started it with Paul McGann dying and then regenerating, with only the classic fans knowing what it was all about, he'd have lost most the audience in the first ten minutes.
He's right, and Sly is right- fans aside, it was simply not a good way to kick things off, and ate up time badly needed by the actual plot!
As for the portrayal of the Master and all this half-human business... meh...