In this Northern location, treatment of your crawl space is very important and you are wise to be concerned about it, and it sounds like you are doing the right things. A couple of points
Putting down a minimum 4 mil plastic sheet over the ground is right on the money. It will retard the upward movement of most moisture. Putting down a second layer is not a bad idea....but I would put down p-gravel on that so that you don't develop a gap between the two layers and the plastic always stays in contact with the ground.
You do not need crawl space vents in the winter. I would cap off any foundation vents in the fall each year, and remove them again in the spring. Insulation between your floor joists is a good idea, but make sure that the crawl space stays above freezing. Also, I discourage putting plastic sheeting up against the underside of floor joists. Every time I have seen this, I have seen pools of water collect on the plastic, often forming large water bladders holding many gallons of water. Not good. Insulating your exposed water pipes with fiberglas wrap or better yet, rigid foam pipe insulators, would also be a good move.