I guess having more than one tag would be better simply because one article can actually fall in multiple category. Also you can do some good on user to tags to get a sense of users interests.
Should the newsletter list the curators, thus giving exposure to those doing the work.
Better even, but with small well knit community to start with, who can sustain with you.
Should I mandate a max or min frequency to the newsletters? For instance, should the curators be poked if they haven't sent out a newsletter in over a week? I think that depends upon how your relationship is with Cratory.
I'd not sign up as its not perfect interest to me but if you start product management i'd do that.
Should I allow curators to enter their own descriptions for the newsletter or just include the link and title in it?
I'd suggest against doing it at start, but later on, with a good set of rules, you should do it.But better part is probably measuring all the emails using the google analytics campaign tagging.