Verb "take", intransitive or causative verb???

Please look at the following sentence first.

"From the moment he comes up with a concept,it usually takes Mr. Barnes a week to produce the finished product"

[Q1] Is that verb "take" used for the above sentence an intransitive verb or a causative verb?
Last night, I thought it was a causative verb. But this morning, after deeply thinking about it, my opinion is changed that it is an intransitive verb.

[Q2] I know I should better use "it" when expressing sentences like the above. But in order for me to understand the usage of the verb "take",
Without the pronoun "it", I want to make a sentence.

a) To produce the finished product takes Mr.Barnes a week
b) A week to produce the finished product takes Mr.Barnes

Which is right between a) and b)? I think a) sentence is right. Because in the original sentence, the thing that the pronoun "it" has indicated is to infinite. Am I wrong?

[Q3] Can I rewrite " ..............., it usually takes a week for a week to produce the finished product"?
I think writing "it usually takes for Mr.Barnes a week to produce the finished product" is absolutely wrong.

Thank you in advance for your teaching.