Winter and Spring are awful time for war with Ukraine in terms of logistics.
First of all, I am far from convinced that there is going to be a war except possible skirmishes along the current line of control.
Hypothetically if a war does happen, I guess Russia's objective is limited to significantly destabilize the Ukrainian government to collapse, a regime change. To do so, Russia does not need to defeat Ukrainian army all over Ukraine (deeply into unfriendly western Ukraine), no trouble for long logistic line in enemy territory. What need to be done is to punch through couple of points of the line of control, quickly defeat some Ukrainian units, go deeply into Ukrainian area, then quickly pull back. This can be repeated many times until the Ukrainian changes course. My idea is essentially a replay of what China did in 1978 to Vietnam. At that time Vietnam did not pull out of Cambodia because the firm USSR support and most importantly Vietnam was not a western democracy. Ukraine today is more vulnerable even if it continuously receives western aid because the government can easily collapse when people suffer enough.