I think at this point, Boyd should be considered outside of the top 5 rotation slots simply because of health.
Alexander can compete for the rotation, I think he’s earned that much.
But I agree that they’ll need two quality free agent starting pitchers. I’m looking at Mize and Skubal in the rotation on Opening Day. I’m not confident in Manning yet, but I think it’s safe to assume the Tigers consider him a part of the rotation. After that, they need the quality major league arms and they’ll need some depth signings to go along with Alexander (could be a multi inning reliever if not in the rotation), Boyd (rehabbing if he returns), and Wentz (Toledo). Another Peralta type minor league signing or two would be wonderful, although easier said than done.