Curated newsletters are only as good as the curator. If you are going to crowd source the curation, even allowing multiple curators per topic, you should allow the readers to also rank the curators. You could do this passively in the email through analytics or more directly with a direct response, such as HN's up arrow.

You should most certainly give credit to the curators! I would also include a digital nanny to remind them periodically to prepare a newsletter. It's easy to forget those sorts of commitments if there isn't a direct reward attached to it.