Congratulations to you!!
To be honest, we lucked into finding the RIU Negril - as it was one of the recommendations from our travel agent. We were really skeptical at first, as the reviews online were all over the place. Trying to keep costs as low as we could for our guests, this one seemed to offer a fair bit of stuff compared to other locations. And, it was gorgeous, our entire group seemed very happy. That said, it really does appear that most of the resorts are absolutely beautiful. We were torn between some locations in Montego Bay, and some in Negril. We opted for the beaches and sunsets offered from Negril over Montego Bay (which is obviously way closer to the airport). We also liked the free wedding package offered by the RIU, as most of the add on items for the pay packages seemed unnecessary. We were happy to pick and choose items to add a la carte. They also let us organize our own private beach party for no extra cost (we had to set up and take down ourselves), but a few decorations, speakers and lanterns made dancing on the beach the perfect ending.
We did find the week actually went pretty fast, as the wedding day was right in the middle. We took a catamaran ride the next day organized for our group which was awesome. I would definitely recommend this. I'm not sure how many activities you are hoping to plan, but it did seem there was a fair bit available - we just didn't look into other activities ourselves. Most of our group was happy with the free activities around the resort (snorkelling, wandering around the fish sanctuary, playing beach volleyball or bocce ball), but I did see quite a few off resort activities advertised. One person in our group did rent a motorcycle to tour around Negril - I would not recommend this, as he came back with some pretty dangerous sounding stories. Or perhaps, just don't rent a bike alone...
I'm sure your agent could help you to organize activities also?