* from a food point of view, every 10C (18F) is assumed to double the reaction rate. Micro is not always linear as in some families will stop in cold, some won’t.
* Mold families are air breathing. Excluding air will prevent normal mold growth. ie A tall container has less surface therefore the risk is decreased.
* Dry ice is expensive and less available. Dry ice produces CO2 gas which in a blanket would prevent growth. Ice is readily available. I would ice to get 40 or 35F and not worry if yeast took a week. ,,, Your heat load is less if you chill once and hold in a clean ice chest. Option, floating crushed ice in a liquid tight bag would both reduce air exposure and do rapid chilling of a must. ,, Option, dry ice added to a cold must in a sealed ice chest would provide a gas blanket.
* There is a major risk of off flavors if there is mold in the must. You will probably not be able to recover from off flavors. A food poisoning toxin from mold is less common, I would taste to monitor.
* A wild ferment is a good choice, note that many cultured yeast will dominate a mixed culture. I would still put the intended yeast in. Do you know the kill factor? Wine is a low risk food. Once you have 5% ABV most food poisoning risk is gone and you have off flavor risks.
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