Thanks, Rebecca, for your great question!
It’s fine to book your room as early as possible, especially if your plans are certain. The biggest benefit is that it ensures availability at the resort you want. The biggest downside is that you'll need to pay your deposit on the room earlier. Please see
THIS Q&A from Bernie for more details on deposits and penalties.
As you probably know, until 2011 pricing is published, you can only make room-only reservations, and you’ll need to do so by phone (not online). Package pricing and online reservations for 2011 should become available during the summer 2010.
To make reservations, simply call 407-W-DISNEY or another travel agency. Personally, I’d book through an Authorized Disney Vacation Planner travel agency like mousefantravel.com or themagicforless.com, as these agencies will usually look for new discounts and offers for their clients and save you money (by adjusting/rebooking your reservation) whenever possible. If you book directly with Disney you might get some extra perks, but you’ll usually have to be on the lookout for new deals on your own.
Regarding staying at two resorts, it can be a great idea if you believe experiencing two resorts will add magic to your trip. Of course you'll have to re-pack during your vacation, which is the part that some people dislike. But if you don’t mind that, then simply take your bags to bell services early in the day, let them know which resort to send it to, and then go off to enjoy the parks. Please be aware, though that your bags may not arrive at the next resort until early evening (usually 3:00pm, but I’d plan for 5:00pm just to be safe). Lastly, I’d recommend reserving the more "special" resort as your second resort, as it’s nicer to “upgrade” at the end of your trip.
Hope that helps!