You are going to love diving with Couples as they are all great.
We go to CN but assume they are the same. Are you taking the resort course only? Or going for your full PADI OW certification?
Either way you will get all the equipment you need with the exception of a dive knife. We bring our own equipment and have a knife integrated into our BCDs but I don't believe that is standard equipment. We also have our own wetsuits but they are not included and you have to rent those for $10/day. Besides the Dive Masters & Instructors we were the only "guests" wearing one. I like to stay warm and it is also handy for protection but no one else had them.
As for the mask; a moustache can be helped with a little silicone or Vaseline to make the seal. If you are going to dive after this trip then I would suggest getting your own mask back home at a local dive shop. A leaky mask can ruin your whole dive and this would turn off new divers. It's a great investment for snorkelling too. We wear glasses so our masks even have prescription lenses.
As for the night dive; this costs $50 and I believe is only for certified divers. But if you do your course the first 2-3 days of your trip you could probably do it later in the week. You should ask your instructor what he thinks as he will know by the end of your course whether you are ready for it or not.
Welcome to the world of diving.
Couples Negril - September 2011, 2012, 2013 and have just booked 2014
Scuba Club Cozumel - Jan, Apr & Nov 2012 and Jan & Nov 2013
Cobalt Coast, Grand Cayman - May 2013
Retiring & moving to Cozumel, Mexico in early 2014