We were married on 10/12/14, the Sunday of Columbus Day weekend. We invited 125 and had 75 guests total, including myself and DH, and all but about 8 of those guests came from Massachusetts or New Hampshire. What's important to take into consideration is when you're getting married vs what's happening at WDW at that time, the habits of your guests (onsite vs offsite) and the hotels you want to block.
We decided to block Beach Club and Pop Century. Since we had an Epcot wedding (9 am ceremony) and a dessert party that evening we knew everyone would be staying 2 nights. Knowing that our wedding was during Food & Wine (and during a holiday weekend) we knew Beach Club would sell out, so when planning we definitely added more nights to Beach Club with the understanding that we could move those particular nights over to Pop if needed.
We ended up blocking 109 nights, with 91 being our minimum guarantee, and our guests booked 114 nights at WDW (we only ended up with 4 guest groupings off property, 3 of whom already lived in Orlando). However I would definitely talk to your guests and try to gauge what they might do. We knew that between myself, my parents and DH's parents we would have 35 nights, so that alone had us feeling more confident about a higher number. We also looked at say, our friends and predicted who would end up sharing rooms. Carrie/Alli's advice is absolutely the smartest, because you can always always add on, but dropping is far more restrictive, so being cautious about numbers is the smartest. What I would add is if you plan on blocking any of the Epcot resorts, focus a good chunk of your room nights there, if only so you can have the space reserved just in case, because those hotels will sell out.
Happy planning and holler with more questions if you have them!