There is no point in insulating crawl space walls, or in adding heat.
The crawl space is not heated and it is outside the home comfort zone, therefore, whatever happens there will not effect the home temperature or humidity once the house floor is sealed and insulated.
Bringing warm air into the crawl space is pointless, if the idea is to raise the crawl space air temperature,to enable it to hold more water vapor and to stop condensation. All this does is to raise the cost of heating a home, at a time when we are trying to save money, the Earth and carbon emissions.
It is perfectly normal for condensation to form on a cold surface that is below "dew point" it happens every day all over the world. Water vapor always moves towards a cold area and/or a cold surface to condense, Condensation forming on a plastic sheet does no harm.
Keep in mind that as the air gets colder as we move into winter, the airs ability to hold moisture decreases, there is less water in the air, once the temperature drops to 40f the air is almost dry, once it reaches freezing the air is dry.
Water vapor always moves towards the coldest area/surface, because of the heat leakage from the home, the wood surfaces that are part of the home are subject to heating by radiation and conduction, as long as the home is heated moisture/water vapor will not enter the structure of the wood.
As mentioned previously the structure of a crawl space is not water vapor proof, therefore as warm wet air arrives outside, and where and if, the temperature in the crawl space is lower, then the water vapor will pass through the various holes in the crawl space walls, floor, ceiling enter the crawl space and condense on the coldest surface, most likely the plastic sheet.