I don't know the hotel. It is a "Beachcomber Group" place so it should be
nice. You will probably be able to dive & windsurf using the on site
franchises, although Gran Baie is not the optimum spot for either
activity.
Beachcomber have hotels on other parts of Mauritius so you could
investigate any "reciprocal" they have with their partners at other sites

If you want to hire a car you will probably find it cheaper (with one of
the majors) on the internet before you go. Just make sure you take three
copies of the hire agreement with you, showing EXACTLY what you will be
paying, your CDW, excess waiver, no airport surcharge etc.

1 to keep,
1 to give to the car-hire desk on arrival
(they will not be able to "find" your rate otherwise)
1 to give to them when dropping off the car.

Make sure ALL the little dents & scuffs are noted on your hire agreement
when you pick-up your car!!!
Otherwise you "might" find all sorts of unexplained extras have been
added just when you need to get to check-in!!! Oh....and the
representative collecting the vehicle will unaccountably have lost the
ability to speak English!

Well known scam!!!

Pip pip

(say hi to the fishes for me!)