You should be fine in October. You can make them on opentable.com if you want. Probably don't need to do it much more in advance than your would your neighbourhood restaurant.
No they aren't.You can make ressies at Opentable.com. However when you can make them depends on the restuarant..Some restaurants are 90 days ,some 60 and some only 30 days out. Bubba Gumps on Citywalk does not take ressies at all