From all i have seen from Rafe so far i'm hugely excited especially him being such a fanboy, i would have had a lot more fears  a few years ago for this but with Game of thrones being such a good show and Shannara being the failure it was, gives them plenty to aim for and know what to avoid. Totally agree that Casting is going to be essential and if you just write Moiraine as the badass she is in the books it will all be fine. The three Boys definitely need to be the focal point, as was said, they drive the story in the early parts and Rand, Perrin, Nynaeve and Egwene  later on so they all need to be fleshed out well early on.