For activities, would you like more of "party" activities, or more like outdoor activities (like snorkeling, cenote swimming, zip lines, etc)?
Because if you would like more of the outdoor type stuff, I would look at resorts south of Cancun, just so you have less distance to travel.
And don't worry, I had a HUGE resort for my wedding, and all of our guests still hung out with each other. We basically just had one place where we'd all hang out. But because the resort was so big and had so many different pools, it wasn't crowded. it was perfect.