I will believe he can hit at the Major League level when he hits at the Major League level. His numbers in Japan are pretty good, but they're in Japan, and no matter what his agent tries to tell you, that's not Major League caliber pitching. A 100 mph fastball is a 100 mph fastball no matter where you throw it. The issue will be can he develop both at a competent Major League level. He is not the first player in history who could hit and throw. There is a reason why players have not been successful doing both. It is so hard to do one well, even dedicating to it full time. I simply don't believe Ohtani has far and away more baseball talent than any individual who ever lived.
As for who's likely to pick him up...if it's not the Yankees or Dodgers, it will likely be the Rangers.
As for wanting him on the Astros, I want any player who can play and improve the team.