Assuming you are going out in 5-15kt winds (for beginner), then you can't get into trouble. The swell will always take you back to shore. It's a good idea to sail with somebody. If you go to Sems, let other sailors know you're a beginner and ask them to look out for you. They should be more than happy to do that. If it gets too hard in the shore break, pack up and go to the Causeway (top of West Lakes) for flat water practice.
Yes, it's a legal requirement. Wearing one of these isn't a bad idea if you are starting out. I recommend the Neil Pryde high hook bouyancy vents (50 or 50S rating). www.windsurfingperth.com.au sell them for about $150.
Welcome back and probably will see you around

J