Honestly I say that Homer starts the year in AAA. If he has 2-5 good starts there then bring him up at that point.
I'm East of you. Be very very worried. Not quite OBX. But, be worried.
If he shows he can throw at least 2 pitches at a MLB level caliber then I'd call him up and let him sit in the pen to work on the third, 1 trick ponies dont last long in the Majors and thats what he would be right now with just the Fastball.
Only way I would try him at closer is if he's out of options and hasnt "got it" as a starter in MLB. Like others have said the risk outweighs the reward.