what are the differences between the following sentences in form and meaning?

what are the differences between the following sentences in form and meaning?

a 1 What do you want?
2 Which do you want?
and what are the categories of "what" and "which"? and their functions?
a 1 What do you want? the speaker here asks and he doesn't know what the answer could be.

2 Which do you want? here, there are limited choices,as if the speaker says which one do you want ? or which book of these "know" books do you want?

the speaker here knows that the answer will be one of limited choices.
"what" is Wh question but i am not sure what is its function.

b 1 They mustn’t think I’m interested.
2 They must think I’m not interested.

c 1 I’ll see Peter tomorrow.
2 I’ll be seeing Peter tomorrow

d 1 If in doubt, call the operator.
2 If you’re in doubt, you should call the operator.

e 1 I’ll do what I think is right.
2 I’ll do it, which I think is right.