I'm a marrone too, but I'm convinced here that all Russian actions begin and end with the fact that Putin and his cronies are robbing the Russian citizenry blind, and their overarching goal is to prevent the majority of Russins from making this connection. That's why Putin murders adversaries - journalists, politicians, and key government figures; and it's why his goons clamp down on protests with extreme predjudice. It's why they lean heavily on propaganda and controlling access to media sources.
Neighboring prosperity represents an existential threat to the kleptocracy, especially Ukraine because it cannot be hidden from Russian citizens. To avoid problems, enact a simple doctrine: Take over bordering countries and obstruct the Russian view of prosperity. In other words, the masses will remain docile if they see that their neighbors like Belarus and Ukraine live out the same ####ty existence.
If Ukraine falls, I think Putin will set his sites on Estonia and Latvia. I know they are NATO members and maybe Putin does not resort to military action in these nations, but I'm sure that there are a thousand ways to be disruptive. If I'm Finland, I'm highly concerned. All the Finlandian sniper heroics aside, if Putin can take Ukraine, he can take Finland.