Hi Amy!
Wishes Fireworks Spectacular takes place most nights during the year (except during Mickey's Not So Scary Halloween Party and Mickey's Very Merry Christmas Party). To see which nights apply during your upcoming trip, simply log on to
www.waltdisneyworld.com. Once the page loads, click on "Parks" and select "Magic Kingdom" from the drop down menu. Click "Calendar" on the left side of page and you will be able to get a month's view of park hours. Choose "October" and once that loads, click on a specific night to see if Wishes is performing. If you see a 7PM park closing time, that indicates a Mickey's Not So Scary Halloween Party night.
As to "park hoppers", I definitely recommend them for their flexibility, unless you are 100% certain that you are only doing one park per day. If you have any doubt, go with the hopper.
I hope this helps and I wish you a Magical vacation this fall!! :)
Chris