The recommended translation (Do you have boxes for books?) demonstrates that English often doesn't have a compact equivalent for Dutch diminutives. While "Do you have small/little boxes for books" more closely matches the Dutch "Hebt U doosjes voor boeken?" it lacks the true power of the diminutive usage. A number of the exercises in this section show the same absence of dimunitive usage in English.
There are some examples where English uses a diminutive, although not to the same extent as in Dutch. They often impart a babyish tone which I understand is absent in Dutch. The two commonest types end in the letter Y or ie and the suffix let. For example doggy, doggie, bunny, bunnie, kitty - booklet, droplet.
Yes, but not in Dutch I think - maybe a native speaker could comment. In Afrikaans (very closely allied to Dutch) 'doos' has the same polite meaning as in Dutch - a box e.g a wooden or cardboard box - ' 'n houtdoos' or 'kartondoos'. It does however, also have a very common use as an impolite word for referring to a fool or an a....hole. A local (SA) golfer, Ernie Els once chastised himself by muttering "Doos!" under his breath when he thought he'd messed up a shot -unfortunately it was picked by one of the microphones and went public (much to the amusement of most Afrikaans-speaking South Africans). [ https://www.youtube.com/watch?v=oXDMB73cq8k ] There is, I believe, an impolite Dutch equivalent of the impolite Afrikaans 'doos', which is also a sexist reference - I'm hesitant to provide this word, as it might cause offence ['offense' in US Eng).
This site is very useful for language questions, once you master enough Dutch to read the explanations ;) I just typed u hebt heeft into the search bar with this result