1/ A prosperous and democratic Ukraine would, from Putin's standpoint, be dangerously attractive to Russians. So his goal may be to militarily divide it up, much as the Israelis have divided up the West Bank, so it cannot function effectively as a state.
2/ Seizing major Ukrainian cities would be militarily costly, so Putin is more likely to want to surround them, controlling access and supplies, making the welfare of their inhabitants into bargaining chips in negotiations.
3/ Such a strategy of reducing Ukraine into a disordered, divided and chaotic mess would drive millions of refugees into the EU, while providing perfect terrain for Putin's criminal cronies to spread crime, corruption and influence into the Eastern and Balkan parts of the EU.
4/ Given the geography of Ukraine I would expect Putin to try to quickly surround the capital Kyev (Kyiv) and the second biggest city Kharkov (Kharkiv). They are both relatively close to the Russia/Belarus border, so this appears a realistic objective. nationsonline.org/oneworld/m…