Disney recently announced that the rest of their resorts will open by the end of 2021. With this added resort availability, now is definitely the time to book. If you would like to visit this Fall, two more value resorts and two more moderate resorts have now been added back to the resort booking menu. This is great news for families looking for more affordable options.
So, when should you visit? The 50th Celebration kicks off October 1st, so anything after this date will be extra Magical, with new rides, parades, fireworks, and extra EARidescence scattered throughout all four parks. Epcot's Food and Wine Festival will run 7/15-11/20. Disney's Boo Bash will take place on select nights 8/10-10/31. So, if you would like to combine seeing the new additions from the 50th celebration with the Food and Wine Festival, I would suggest sometime in October so that you can also book the Boo Bash.
However, I absolutely love Disney at Christmas. With this in mind, I would wait until November to visit. Decorations are usually up by the second week in November. This way you can also visit the Food and Wine Festival while you are there. December is still showing quite a bit of resort availability, so, this would also be a great time to visit. I am also very hopeful that Disney will offer some type of Christmas Party this year, I really miss the snow on Main Street USA!