They really need to not rush him. There's going to be a big deal about him- there already is- but the worst thing is for him to believe his own hype.
As for Greg Chappell's comments that he should play in the Ashes, it's rubbish. He, as yet, doesn't have the numbers or experience to back him up, and there's no one to drop either.
A couple more years of Shield cricket under Warnie's tutelage making him first and foremost a leggie and he'll be good to go, but not yet. Don't forget that Warnie didn't debut until he was 22, and Smith's still only 20.