Since we can create multiple portals, can we choose to have different News at different portals?

I don;t think so. You can choose the current forum you want the news to come from by going to admin panel=>Modules=>Portal & Calendar=>Configuration and look for the " Board of the news" option. Since you can't use two portal pages at the same time, I think it might be better if you choose a forum that you want for the news for the current portal page, and then when you change the portal page, you can change the news forum as well.