No. I'm sorry, but no, if you're going to say "one hundred", you HAVE TO accept "A hundred" as an alternative. For crying out loud.
I agree absolutely. This was marked wrong: "Last month that comedian bought a hundred rabbits and now he is broke"
"and is now broke" is a legitimate rendition of the last part
No need for đã here?
No, because the tense is already clear from "last month"