I am not convinced of a full scale nuclear war but a tactical nuke to achieve his aims is definitely a possibility.
I do agree that Putin is not "crazy" in the common-use sense, nor is he delusional, stupid or about to die of cancer. He probably is a sociopath but that is another issue.
He does however understand power politics and the power Russia has, given it's vast fossil fuels resources and increasing arable land.
He is not good at sharing.