Modern sites - news webpart limitations

For 1) Try using the + Show/Hide columns option in the All Pages view of Site Pages. You can only expose Promoted State from the "modern" experience. Once you have it showing, you can group by Promoted State (again, from the modern experience) and then use Save As to save the view. I usually save it to All Pages and then make that the default. That makes it easy to find News pages.  I haven't found a way to do (2), but should be able to add a SortOrder column (it might have to be a site column) to the library and then map it to an available RefinableStringxx column and use Highlighted Content to create your own list of articles. For (3), I've been using Highlighted Content to organize news articles and filter them with naming conventions (e.g. People Spotlight) but if your site structure follows "the world is flat" model, it won't matter whether news is site or site collection - because you won't have sub-sites. Once Hub Sites are available (Q1 2018), you will be able to roll up news from a family of sites on to the Hub. And from SharePoint home, users see all the News from sites they follow and those suggested by the Graph. News experiences are evolving but with some planning, what we have today is a really great start.