Davis' bat will play very nicely at DH. I don't want him at 1B unless he can play an above average defense. I would give him about 80 games to show what he can do, but if he's consistently costing us runs there then we will need to rethink the lineup.
There's very close to a 0% chance that he can be above average on defense. Even average is an extreme long shot. He's bad at defense. People who are bad at defense don't suddenly become good just by playing more.