Good luck. I was in a similar position, but my garden was less jungle, more shady bare patches from so many trees. I spent some time researching what would grow in shady, dry areas and did a bit of experimenting. As you are near the coast, I am sure there will be specific plants that will thrive in your area and soil. Check out the RHS book of plants, it lists this sort of thing. As many others have said, divide you garden into plots /areas and work on one or two at a time, you can always go back and change or develop it in the future, thats the fun part!!