Should I remove cold cellar wall insulation below grade to allow ground heat to warm the space in winter?
I think you are safe with the conditions you explain, however if you remain concerned, (you are the one who lives there.  I do not live in your climate), I would start by restricting the size of the air vents. Your goal is to do no more than to keep the air fresh without dropping the temperature below a safe level. You could install a freeze control alarm for the area.  Keep in mind that if the sump is buried in the ground it is a good deal warmer down there, (I would say at least 5*) than the room temperature is. When it is all said and done, it is your house and your concerns. My comments are simply that, comments; from someone who has been in and around this type of business all my working life, 40+ years. P.S. Can you do anything to mitigate the smell. (I remember hearing it said once: In a multitude of counsel there is wisdom.)