Welcome to the sport trippnu. Best advice I can give to anyone starting up is have some lessons, there are a few schools listed on the WQ site
www.windsurfingqld.com/links/lessons.aspx or failing that just buddy up to someone and ask where the sharp rocks are. Both Manly and Wello have their fair share of oyster clad rocks and the trick is just to know where they are and avaid those areas.
There are a really good community of sailors at Wello and Manly so you shouldn't have any trouble getting the low down before you go out. There are also a number of clubs on the site if you want to sail in a group setting and draw on the experience of the other members.
Hope you stick with it, it is an awesome sport to get into.