What size windsurfing board and/or windsurf sail you get as your first setup depends on a few factors:
1. How much windsurfing you have done
2. How often you are intending on windsurfing once you have the equipment
3. If you have had/are going to have any tuition
4. How quickly you tend to progress / natural flare for windsurfing
Here at the Poole Windsurfing School, we sell on our last seasons kit to make way for brand new equipment each year. Currently we still have an RRD Evolution 180lt windsurf board that is great for the basics & moving onto learning faster tacks/gybes, beachstarts, harness, planing and even footstraps.
You do need to be careful not to go too small in volume with your first board, else it will slow your progress.
Our second hand equipment list can be found here:
http://www.poolewindsurfing.co.uk/special-windsurfing-offers/used-windsurfing-equipment/Happy Windsurfing!