Congrats and welcome to the forum! My FI and I will do the legal part of it before we leave for our Mexican wedding as well, to make things easier down there.
Good luck planning.
I'm going to have my wedding at the Gran Porto Real. Personally I liked having the Royal right next door. That way if some guests want a kids-free vacation they have that option.
I didn't look at the Iberostar Paraiso Maya so I can't help you there. Good luck planning.