I think waitz does it the right way.
Looking at some deals, that could be good, and then asking if experience with these very ones !
As he is relatively new, and totally new in waves, it does not make sense to "get what you really need" - as you havent got a clue what you need nor wants....
That will take some years.
If experienced it was another matter, and I agree - get the thing that works the best no matter what it cost - you wont regret.....
But this is not the case here - and if, he would not ask what to buy
You can also go for the bigger Whip, as a light wind board, true
So important that you decide whether you want a dedicated light wind wave board, or a board for overall wave condtions too.
You live in the same wind region as me (Denmark here), so your conditions are pretty known.
Low pressure systems passing by, so you got loads of wind in the autumn and winther and often in spring.
And in the summer you can have awesome wind for small kites, but also weeks with high pressure systems (your family will love as it is the "good" weather for them, while you get more and more cranky) and very low winds.
And you can have good seabreeze wind conditions in spring and early summer too at the coast of Holland, just like we have.
So a 12m2 is perfect for your max size, and you dont need a bigger one not even for summerdays.
I think I am the only one here who are crazy and sometimes ride waves with a 12m2 - that is simply not "normal" with these sizes.
Nor easy, but with years of practice one can do this.
Although - I understand fully those (almost everybody) who would never touch a waveboard with a kite bigger than 9 or 10m2
Maybe Supaez is right, the 5'4 Whip is an okay allround waveboard as not that big - and with the 5'8 you got a board for light wind mostly (thats what the guys here use it for, but never when windy).