Welcome SJ, you know one of the best things about SUPping is that you can paddle just about anywhere.
Think about what you want to achieve, what you want to see, who you want to do it with and pick a spot. WA is full of all sorts of places to give it a shot.
If you are unsure pick somewhere quite with a minimum of chop, as you progress get more adventuress.
Always think about your safety and in particular the safety of those around you.
SUP's are big, hard and can be heavy.
Have fun.
ET.