Finally, gardening is as lucrative on the beach as it is anywhere else! So if you collect all the seeds available (especially from festivals in City Living) and start planting, it is a sure-win way to get rich quick. But then, your game play will be real tedious and boring.
Roses and Birds of Paradise are the easiest to obtain and have the shortest bloom cycle. I usually skip Dragonfruit and Alien plant just because they are hard to find at the start.
And I like to grow coconuts and pineapples to store in my Sim's inventory. It helps to just eat those while you swim around Sulani so that you travel back all the time to eat.
Fishing is good way to get cowplant berries and treasures of Sulani right from the start. Sell them ALL. And you will quickly have money for your basic needs.
Child of the Ocean Sim will feel wretched fishing though. In the end, my Sim never fish because of the lousy moodlets from it.