As with my last post, It is quite clear form the get go for the Russian to lead a "North/South" charge and link up between Northern arm with the southern arm form Crimea .So I would have to say the the keys for Ukrainian defence is going to be to defend both Dnipro (in the south) and Kyiv (in the north)
The problem is, Russia as of now is already seriously behind. Current intel suggested a 96-120 hours delay. Objective that supposed to be taken on the first day is still in Ukrainian hand. Mariupol, which specifically were supposed to be deposed in the first minute of battle, still stay with Ukraine., Kyiv, a day 2 at most objective is still stand. Dnirpo are virtually untouched. Kharkiv is not yet fallen. There are even news that Antonov Airport are under assault by Ukrainian army. All these are the strategic objective, and they are not yet taken, in fact, the only "Major Milestone" for Russia is taken Berdiansk, a city of less than 100,000. That is not a good time table.
So two things is going to happen. The war is going to have to speed up, which mean more Brutal Russia response, which in turn mean more resolve on Ukrainian resistance. And another thing is going to happen is Russia is going to pour more resource into Ukraine.
Now, the problem is, what people see the problem Russia is suffering is command and control problem and logistic problem and it is not going to solve itself just because you need to hurry up. In fact the entire system failed because they were in a hurry to begin with. So that have to be rethink. All these tanks that ran out of fuel cannot be happen again, and LOGPAK are going to be delivered into the right place on time. That will stress the entire campaign.
On another thing, more unit got thrown into the fray will magnify the C&C problem and also the logistic problem. That would have to be an issue, how are you going to pipe in reinforcement? Send them to where they needed the most? That is THE problem.
Another issue is that Russia need to think about what happen after they defeated the Ukrainian Defence Force in a conventional battlefield. There are VERY HIGH chance that Ukrainian are going to wage an insurgency toward Russia. Which I can assure you whatever left of that Russian force is not going to be enough to deal with. You also need to think of how to contain such insurgency, now, traditional wisdom would suggest you need to get the entire country in control, and then squeeze the insurgency out. But Ukraine is a country that have 1/3 the population of Russia, I would say except for the Eastern Ukrainian, almost all of them are going to be hostile to the Russian. And I can't see any way Russia can conquer the entire Ukraine, which make Western Ukraine more important than Eastern Ukraine, because this is where it border Poland, Romania and Hungary, that entire region needed to be occupied, otherwise Western Ukraine would become enclave of Ukrainian insurgency activities. Which mean the entire troop deposition as of now need to shift West once Ukraine Defence Force is defeated. Do they even have time to do that? Unlike what we did back in Iraq, we enjoy a honeymoon period, and then half life set in, and the entire country turn on us. In this case, there are no half life, there are no honeymoon, the entire population of Ukraine is going to be hostile to Russian.
And finally, the economy sanction factor, unlike the other, this is one giant swoop. It basically destroy Russian economy and its banking system. And it will take them ages for China to restore it for Russia, on the other hand, would China want to? Because that would include a lot of financial backing, which at the current rate, mean backing a rouble that is currently down at the toilet. Effectively it would probably cheaper for Russia to adopt Yuan as official currency.