I wasn't brewing when I lived in New Jersey, but I remember the winters! I even learned to drive in the slush and ice. 57F is ok for storage and just slows conditioning a bit, but unless there is some heat leakage into the garage, I'd be concerned about freezing later in the year.
I just proof the yeast, I don't do starters, except maybe for high gravity ales. Even then, I may just add an extra package of dry yeast to whatever I'm using for that batch. And I never hesitate to toss in another packet if I think the fermentation is stuck.
Maybe you could wrap insulation around the water heater & reduce the temperature in that room? Or keep the starter near the floor (but protected from beer drinking dogs).
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