Hi and welcome! Congrats! We just returned from Sandals in Jamaica (Ocho Rios, to be exact) for a little winter getaway before our wedding April and we hit the one week of January where it rained all day long. Hopefully you have much better luck with the weather. And for the record, it is supposed to be dry and sunny all through January, but we just had bad luck.
Anyway, about the wedding, you would have a great time choosing Sandals. However, just a couple things to know about them that may impact your decision (as it impacted ours when choosing the resort) is that (1) they do multiple locations per day, (2) at least at Ocho Rios, it was packed with very little beach property to host a wedding, and (3) the nicer ones were those that rented a private room but obviously those are more expensive.
Even though it rained, we had a great time, and it is nice knowing that it was all adults at Sandals.
One more thing - I see you are set to get married in September? You may be able to strike up some good deals and it may be less crowded since hurricanes notoriously hit the Caribbean at that time of year.
Best of luck and welcome to the forum!!