Congratulations, sarahsmom3! Now to get the countdown ticker started!
First of all, you will be going during Value Season, that room is at it;s lowest rack rate. Keep an eye out for room-only codes and you could get it for even less. The codes for late August should be announced sometime in late June to mid-July.
As far as the tickets are concerned, just about anyone can and will beat Disney's price for the tickets with more days and more options. I'm partial to
Ticketmania because they do have pretty low prices and they ship for free. Other good ticketbrokers are
MapleLeaf and
Discount Orlando Vacations . You can also sign up for the
MouseSavers.com Newsletter . Mary frequently has a link in it to discounted Ticketmania tickets. The newsletter is published the 15th of every month. The tickets for more days with the no expiration option are less expensive per day than the 3-day MYW base passes that you're considering. If you plan to return to WDW within the next couple of years, I would recommend getting a 7-day or even 10-day non-expiring passes.
For the dining plan, you would have to book a package. You cannot book it separately. Right now, if you do that, you will pay the rack rate for your room and Disney's advance-purchase price for the tickets. It's worth considering if you plan to do one sitdown meal every day. Both Cinderella's and Chef Mickey's count as sitdown meals. I priced it out for my family (2 adults & 2 juniors) but at $140/day plus the higher ticket cost plus the increased room cost, it came out to close to $200/per day. So for me, it isn't worth it. In your case, if you decide to go with only the 3-day MYW base tickets and don't want to wait for room codes, the added cost of $80/day might make it worthwhile. You would need to crunch the numbers.
I hope I covered all your questions. Don't hesitate to post again if you have more! Good luck with your planning!