Guys please don't amuse yourself: there won't be any real fight between Russian and Ukranian militaries that clearly marked as such and allowed to act as such. Putin is not a master of war, he is an avid explorer of specops realm. Let alone Ukranian leader Vlad Zelenskiy who uses every opportunity to calm the rough seas.
Of course Russain Army dominates Eastern Europe but Russian economy wouldn't support any war: Crimea, Donbass, Belarus, now KZ and most of all Chechnya are too expensive to Russia on everyday basis, and any war will break already weak economy within weeks. It may be far from evident but stability of Russian currency is not linked to a storages of gas and oil: since both pumper and pipeliner are under state's control, Russia cannot influence stock prices by volumes, like Saudis.
So, please note that each time we are buying buckets of popcorn watching Russian news, there something is going on around China - unnoticed and unexplainable.
I think Putin sees a narrowing window of opportunity to act in what he considers Russia's, in reality his own, best interest. With a Ukraine that is becoming more independent from Russia every day, slowly but surely, Russia's military reforms bearing fruit and a Europe that is still dependent on Russia for gas this is a pretty good time to act for him.
While the Russian economy will likely suffer as a result he doesn't have to take over all of Ukraine to 'win', at least for him. A short, sharp campaign to 'punish' Ukraine for its intransigence will still be effective in sending a message to much of Eastern Europe, while fearful of Russia isn't 'dominated' by any stretch by them, not to go against Russia's interests. And while sanctions and other measures might take a bite out of the Russian economy the reality is that there is only so much pain Europe is likely willing to endure and most probably don't care enough about Ukraine anyways to hold the line too long. A geopolitical 'fuck around and find out' by Russia if you will.
Remember, Putin is not Napoleon, Friedrich der Grosse, Peter the Great, Winston Churchill or George Patton: he is rather kinda Richelieu or Pope Alexander VI Borgia, his victories are not military ones but political firstly.
Putin doesn't need to be Napoleon to or any other great military leader to occupy much of Ukraine, even with reforms over the past few years the Ukrainian military isn't unfortunately that big a threat to Russia.
The main reason to hope there won't be any war is that with essentially no smart weapon in both adversaries' possession, collateral death toll will be terrible on both Russian and Ukranian soil.
There are plenty of Russian weapons that are smart enough, and Putin has proven from Chechnya to Syria that he doesn't care too much about civilian casualties.