everyone has different perspectives on this, if you do a search you'll find there are several threads on the topic. We have taken the anti-malarials any time we are coming for an extended visit and plan to be off the island very much. I am a mosquito magnent and it just wasn't worth the risk for me. Out of the four of us none had any adverse side effects at all, but I have heard complaints about side-effects from others. I don't take them for short trips when I'm not planning on leaving the island.
Deet is still pretty much the best as a mosquito repellant. All the studies I've read say the only difference in terms of percentage is the length of protection; i.e. 4.75% DEET provides about an hour of protection, 23.8% DEET about 5 hours. 100% will protect for up to 12 hours, but you would have to reapply after swimming or bathing anyway and it's pretty harsh stuff so I wouldn't reccomend anything higher than about 30%. We love those OFF towelettes, much easier than a spray. I think everyone agrees you should get the hepatitis innoculations.
I drink the water from the tap, have never had a problem and think it tastes fine. Some will tell you it depends on where you stay.
Everyone travels differently - do what you need to do to put your mind at ease and then go with an open mind. You'll have a great time!