I think 3 days should be plenty(especially with FOTL access). I went last February and walked onto EVERYTHING. My friend and I hit every ride in US(most more than once) within about 5 hours. Then it was off to happy hour!
We did the same thing the following day at IOA and used the third day to hit our favorites one last time. I'm going again in October but decided to do 3 nights- 4 days so I can include Halloween Horror Night. Enjoy!