Good to hear you have such an abundance of quality material around, and being a landscaper will make it even easier. Choose a tree with an interesting, curvy trunk and go from there. Since it's so available to you, probably start with a few trees so you can experiment. For me, the most difficult thing with rosemary is the wiring. Since WIRING IS THE SINGLE MOST IMPORTANT SKILL IN BONSAI, this can be problematic. The older growth is very brittle, so new shoots must be wired when they are still young. There are many quite charming examples of rosemary in our local club ranging from bunjin to cascade, so there are a lot of possibilities. Try to find a club/teacher in your area to join and learn from. Good luck!