Agree, body weight + 10 litre is hard the first times, but possible.
And when learned, eventhough you CAN go small when windy, you will still love having the size when wind backs off and you have to stand up rescuing yourself to shore.
So one size you can use while learning, and later
When learning you should ride a bit too powered anyways, much easier.
Dont go out when its low winds, on a small board, when learning.
For very beginners, body weight + 30 litres is by far the easiest, though, if one had the option.
But you will catch it very fast so using + 10 litres is quite possible also, and you dont need to change board later.
You might of course end up having two boards, + 10 litres and a smaller one for really windy days or with more stable winds.