Advice for honeymoon in St Lucia?

After looking at various carribean destinations I have settled on St Lucia. (He wanted to go to Fiji or somewhere similar, but I don't want to be on a plane that long and want to make the most of our budget.) I look forward to doing excursions but also relaxing on a beach. I've been using Trip Advisor primarily to look at hotels and things to do. I am thinking about doing 3 nights on the north end of the island and 4 nights on the south end in order to do some of the popular excursions that only leave from the northern hotels but also see the Pitons and nature stuff in the south. Is this a good plan? What are the must see places or things to do? We have never travelled outside the USA. Is St Lucia a fairly safe destination (as traveling abroad goes)? Should we rent a car or pay for taxis? Any favorite resorts/hotels? I'm nervous about scheduling such a huge trip. Any advice from someone who has visited St Lucia is greatly appreciated! TIA