With the airlines now charging for checked bags, it is quite common for guests to send packages ahead to their WDW resort. Often this includes diapers, wipes, or other bulky items, but you could even mail your clothing to yourself if you wanted.
I spoke with the front desks of three WDW hotels and none of them were aware of any specific size or weight restrictions associated with guest packages at the resorts. To get the correct mailing address of your hotel, you can look on the resort-specific WDW website. For example, the address for Disney's Caribbean Beach Resort can be found on the far right side of the page
HERE. If you prefer to call, you can get the mailing address for any resort by phoning 407-W-DISNEY.
When addressing your package, it helps the hotel if you can include the word "GUEST" and your arrival date on the front of your box.
Have a wonderful vacation!