See I think the calculus in a question like this is to find the player or players who are the least proven, but with the highest upside. A guy like Inciarte isn't going to give you a 5 WAR season. He is what he is: a solid 3 win CF who relies on great defense. His value has been remarkably consistent over the years and I think we can feel comfortable in him doing the same thing this year. I'd also take Newcomb out. He still has a lot of questions to answer about his game, but I think we can safely assume his floor is around a #4 starter.
I'd also take out Freeman, Acuna, Markakis, Flowers, McCann, Donaldson (tentative on health), Teheran, Gausman, Folty, and the bullpen. There are questions surrounding some of those guys, but most of them have established some sort of value window i.e. the best we could expect vs. the worst.
That leaves guys like Ozzie, Dansby, Camargo, Riley, Touki, Soroka, Wright, Wilson, Anderson, and Gohara. That is the group that I'd be inclined to pick from because so much uncertainty surrounds them. They all have the upside to be stars, but still a generally uncertain floor with maybe the exception of Ozzie.
Now that I think about it, the correct answer to this question may be Allard. If I had a magic wand and could turn one player into a star, I think he'd be the best choice. He's the least likely of all our top prospects to produce anything notable on their own so if I could give him some magic I'd feel comfortable allowing the rest of our guys to develop and provide value on their own.