Hi,
I've been to the maldives four times so can anwer your questions fairly easily.
Tips are up to you and of course depend on the level of service you recieve. I usually give $15 a week to our room boy and waiter and then $10 here and there for bar staff.
Never had any vacinations for any of our trips and you are now getting to the stage where if you had some they would have time to be effective anyway.
The sun is much, much stronger in the Maldives then in Tunisa and you can get really burnt on even a cloudy day. I have quite dark skin and start off with factor 20 and work down but never do below factor 8. If you have fair skin you should start at factor 30. Buy it before you go as it will be very expensive to buy there - as everything is in the maldives as it is all imported.