I have been paddleboarding for 3 years now, I windsurf too.
You will love it
I use a Naish Mana 10 foot board, but 12 foot is a good size too it will track better in the water than mine.
A few tips to get you started, stand with your feet a shoulders width apart in the centre of the board (where the carry handle is) keep your knees bent, don't look down but look forward in the direction you want to go & and lastly if you start to wobble just dig the paddle in the water and pull it back towards to you so that you can steady yourself.
One last thing get the paddle adjusted so that the height of it when vertical is 150mm taller than the top of your head.
Most of all have fun
Hope this helps a bit.
Cheers all