SXM

Yes... but also breezy! Dress comfortably

We will create a group chat in "What's app" once we know who all is going and will use this to communicate with.

It depends how much traveling around the island you want to do. There are taxis and shuttles if you stay at a resort or the bus system is cheap and easy to use but if you get an air BNB, I recommend renting a car.

Euros and dollars- everywhere takes dollars. Bring some cash but credit cards will take care of you at most places.