re: Are teams required to announce their starting pitcher(s) for the weekend?

I don't know if there is a hard and fast rule, but I do know that generally the managers give the lineups to the media (TV/Radio) at least 90 minutes before the first pitch as a courtesy so the announcers can prepare and the crew can prepare graphics, info, etc.

Hell, you saw last year Alabama didn't announce Holman was a scratch for Game 1 until pretty late on Friday. Of course, the coach had an ulterior motive for doing so