I stayed for shabbos, was beautiful and Chabad had a nice minyan (during jan vacation week at least) and absolutely delicious and plentiful meals for free (though u should give a nice donation as they don't get funding from Chabad general). Not sure if this time of year is busy enough for minyan there, but also ask kosher luxus if they are having minyanim (I think they also have shabbos meals but they charge). I believe they are more sefardish (as in adus mizrach, both for food and minyan). Definitely get in touch with Chabad rabbi and rebbetzin, they are so helpful and nice.
Re staying for shabbos, I had stayed in the lagunamar all week which was wonderful, but chose to switch to the aloft for shabbos since it was much closer to the Chabad house (45 minute walk vs 5 minute walk) but the aloft is really a heavy downgrade vs the westin lagunamar and peeps we knew who stayed there for shabbos were much happier. Can pm me and I'll provide tons of detail as info on kosher etc in cancun, meant to do a TR with instructions on where to get what etc but some peeps told me not too so the place doesn't become miami (and theN the value will godown).