First what i do is place a car and people ferry on the island you are one. On the next island place another one.
I usually place a wind turbine for power and it works well. After that you should add a marina next to them. It increases more usage from smaller islands. For example you have 2 main big islands 1 small and many tiny ones. On the 2 big ones you add both car and people and only people.THen on the smaller island put car and people ferry. The when you get to the tiny islands just add a marina.Hope it works 4 you!
Daytona-nights