No advice on the medical side but wow you're in for a treat! Which island are you going to?
On the holiday side if you like snorkeling buy your own mark before you go from a specialist shop, guarantees no leaks which makes the whole experience much more enjoyable.
The staff are always very obliging so if you need any extra help just ask.
Any advice on the maldives just ask I love it there!
I'd have to check the fish out... not always keen on them around me lol. OH lives fish and used to keep marine tanks. So I will tell him. Would snorkelling use a lot of energy- thinking of hypos which I'm a bit prone to