How difficult is it to drive between major cities (Poznan, Wroclaw, Krakow, Warsaw)?
There is a huge traffic between major cities so snow have no chance to stick to the asphalt. If you don't exceed 80km\h you will be ok but it is boring. Keep the distance. Periodically try brakes gently for a black ice. Avoid driving beetwen lorries.
but am just concerned about road closures
Main road closures don't happen except when there is a serious accident.
Have powerbank with you to charge phone or navi and windscreen de-icer, high visilibity vest inside of cabin.
Beware of wild boars in the night.