Maybe I'm being naive, but I dont think they can hold the country if they take it over. To control a country you need to control all the major cities. And to do that, you need a massive amount of boots on the ground. They don't have enough numbers, and the Ukrainians are not going to accept it.
They have to hope the Ukraine surrenders , without going into those cities.
More than likely surrounding them with big numbers , getting what they want then retreating.
I suspect that it will just start a movement of terrorism within the Ukraine , Russia, and Belarus, there are over a million and a half Ukrainian people in Russia for instance.
Couple of hundred well trained people could cause a lot of problems , pipelines cut, car bombs ect. More than likely with covert training from the Western powers.
The Ukraine people are proud can't see them meekly just taking a hiding and letting it go.