It's close. Basically, you're betting that Hill will be the full-time starter, while Grace will platoon. Sounds like the odds are on your side here (although neither is certain), but I'd keep a close eye on Hill (and Ortiz), and start considering a backup plan in case Hill doesn't work out. I like Hill's potential a lot, though.
One more factor to consider is: what salary will be assigned to whoever you pick up to fill your roster?
Anyway, looks like a solid move!