1) Its very easy to plan your own travel to Bali. I did that when I last went. Bali is a very small island and very easy to get around. No point letting the travel agencies earn ur money. You can book accommodations directly quite easily.
2) The island is surrounded by dive sites and the good ones congregate around tulamben area where there is a wreck just off the shore. but i do believe that the whole area is a marine park. In any case, please avoid taking anything from the ocean. Be a responsible reefer/diver.
3) good quality accommodations are aplenty... but very expensive. You'll find most of the 5 star hotel chains located @ jimbaran and nusa dua. i suggest inter-continental and ritz-carlton if $$ is not an issue... you'll definitely be very pampered. Otherwise its also quite easy to find rental properties for short stay that comes with a housekeeper (who also cooks) and driver.
4) definitely easy to find good massage on the island but once again, they can be very expensive.
5) avoid places with caucasians if u dun want to get bombed... just kidding... i think the island is relatively safe (and everything is predestined) but of course, probability of getting bombed is higher in crowded places for obvious reasons.
6) surfing is good on many of the beaches but the most popular one is probably kuta
7) to enjoy the cultural side of bali, ubud is the place to go. you'll find art galleries and museums here
8) please bargain, otherwise you WILL be ripped off...