I thought I read somewhere that they were not going to bring back cast members just as a cameo for an old fan favorite. They said that if they were bringing back characters, there had to be a valid reason in the storytelling.
They sold this as more than a warm-and-fuzzy reunion show.
I'm not an expert on streaming but it looks like you can sign up for some of these streaming sites (such as CBS Access) through Amazon Prime (they call them Channels). I'm thinking that these can be accessed directly through your Prime app, rather than needing to download another app and...
EW is not a fan of the first episodes:
Can Star Trek: Picard recover from its bafflingly bad premiere?
https://ew.com/tv-reviews/2020/01/23/star-trek-picard-review/
So this must be a limited series "one and done" event? The promos on today's football games have been that Picard "comes out of retirement for one last mission."
Unless they're going to drag out that one last mission for multiple seasons.
A lot of people had similar thoughts years ago with the less-than-stellar reaction and plummeting box office for Nemesis showing that the TNG well was running dry. But here we go again....