Hey Howdy Hey Jenny and welcome to planDisney!
I bet you all are getting super excited about your Magical vacation just days away at this point! Thank you for your questions about entering the parks. I will be happy to give you more information on both options.
When it comes to visiting the Walt Disney World Resort in the fall,
Mickey's Not-So-Scary Halloween Party is one of the big events that will bring so many to the parks. While this party does tend to sell out quickly, it is rare that Disney will release more tickets for the event. While this is rare, you never know what kind of Magic will happen so keep checking back and it may not hurt to ask about availability at the ticket windows when onsite.
While the Halloween party is a big reason for many to visit the parks, they typically do not get so busy that they sell out of regular day tickets. Park Hopping usually is not affected outside of the Halloween party nights either. One thing you can do to get a better estimate is search for "Walt Disney World Crowd Calendar". You will be given several options and these can give you typical estimates of what to expect in the parks with attendance using historical data and special events. These can help you plan your trip and park sequencing based on the crowd levels.
Best of luck on your final days of preparation for your upcoming vacation. Please let us know if you have any other questions, we are always happy to help!
To Infinity and Beyond,
Nick