Not a bad choice. He has the build and features. Though I thought he was kind of on the short side for Superman (though IMDB lists him at an even 6 feet).
Considering the season finale of Supernatural is less than two weeks away, I think there would have been an announcement if it was going to be the series finale. I think Season 12 is guaranteed.
In addition to Supergirl, the CW also ordered three other new series for fall, so they're likely...
From TVBytheNumbers.com:
It generally adds about 50% in the Live+7 DVR ratings calculations, so that might bump up to a 1.8 after a week's DVR viewing.
Overnight ratings ticked up a notch this week to 1.8 (vs. 1.7 week ago), so maybe it's stabilized. That would put it in the same neighborhood as Gotham which is pretty consistently 1.5-1.6 each week.
CBS projects that DVR would add about 65% to the rating. So that's, what, around 3.6?
It's rather amazing how much some shows add (some double their live rating, or more) when considering DVR. That's why some low-rated shows seem to stick around.
A few samples of Live+7 DVR for Oct 12-18...