Where do start ? :)

I guess it comes down to your friends definition of 'tropical' - get him/her to show you photos from articles/web pages that appeal, and work from there.

My own preference is to use a combination of natives and exotics, but it comes down to finding what works. The key is microclimate, and that means establishing effective barriers to sun and wind which dont completely block either (if that makes sense) - airflow through the garden is very important (as it is with any style of garden).

Good soil is particularly important in a tropical garden - palms and other tropical plants are heavy feeders and do best in a deep, rich friable soil. We all know the deal here - lots of compost, gypsum for clay soils etc. The Sunny Coast is famous for the quality of its soil, so you should be on a winner there. Colin Campbell claims that it doesnt hold water terribly well, so the compost remains a good idea.
My planting tip is to put in as many advanced palms as you can afford, as they will give the garden an established feel from the outset. From there its a case of choosing the underplantings, and that comes down to the usual practical and aesthetic criteria. Many tropical gardens have been built on a small palette of proven standards - cordylines, crotons, gingers, bromeliads and ferns - but the sky is generally the limit. Find out what works in your area and go with it - its easy to become fascinated with some of the more delicate tropicals, but old standbys like Tradescantia really earn their pay when conditions get tough. I've also had a lot of success with Diffenbachia and various Philodendrons - your mileage may differ. Layering plants, tallest at the back and smallest at the front (ok, ok .. ), is usually pretty straight-forward with tropical plants, and it will give you the best combination of privacy and shade.

Jan, I suspect that you know a lot more about gardening than I do - tropical gardens are simply another form of cottage garden, IMO. As with any mixed planting, how you group your plants determines how effective the overall vision will be. Combining plant choice with effective placement is where it's at for mine - things like water features, follies (bridges/ornate doors etc) and statuary can usually come later.

Good luck,

Artie