Area I -
Including enough detail to keep things real is an important task of world-building. By introducing your PCs to a completely different situation, you've doubled your workload. Advice: keep your gameplay area in the New World very small. The PCs tasks to complete, and way to get home, should all be found inside the small area you designate as the roc-destination. Say, one village only.
Area II - I realize I'm condoning the situation by saying this, but you'd be better off having Grush drug your PCs and throw them onto a caravan headed for the New World. But if Grush is the kind of guy whom the king won't send his army after (even to rescue his own daughter), he probably DOES have a roc at his beck and call.
-Heinrich smiles. Cynthia smiles. Hermit attacks!