Let's start with you main mistake (and, since you are not from Russia, you are likely to make this mistake): Putin does not care about the well-being of Russians. What he cares is about is his ego, his power, and his money. He likes to win, so, he plays by the rules but he plays dirty. He does not want to simply invade Ukraine, he wants to get what he wants without breaking the rules but stretching them as far as possible and he remains the judge of whether such stretching is allowed. But in his own world he always believes that what he does is right and he does not break any rules. Also, such "win" increase his popularity inside the country where many people also fill that they are "winning" (despite the economic losses they will suffer). In some sense, these Russians are like you or Franfooter: you are happy when your side "wins" and this is the only thing you care about. You are willing to overlook any stretching of the law as long as the letter of law is not violated: I do not believe you are so dumb that you truly believe that non-violent demonstration, even if it is lasted for 3 weeks and includes road closure and noise is truly a national emergency that warrants Emergency Act (again, you will argue that it does not contradicts the law and it helps makes things easier for the government, but it is just another way to say that JT stretched the law to make it easier for himself)
Now, back to Putin: Putin does not care about sanctions for 3 reasons. First, these sanctions affect ordinary Russian people, not him, and he does not care about people. Second, he knows that U.S. and the West will be afraid to go after him personally. And, third, he knows that Europe is not willing to bear the costs of thigh oil and gas prices and will never embargo Russian oil and gas, so, he will always have enough money to do what he wants.
The reason he did not invade Donbass over the last 7 years is simple: he enjoyed his "win" over Western world from annexing the Crimea for 3 years. Then he enjoy playing " Ukraine doe s not want to follow Minsk agreements" for a few years. Then he needed NS2 to be built, so, he backed up a bit. Now he is pissed that he had to behave the last few years and he wants another win. So, he gets it. It is like with fine food: why don't you it 20 stakes in one sitting? Because you like to enjoy them and spread them around a few weeks. So does Putin. He simply enjoys it. What else a dictator with large nuclear arsenal can do (and world destruction is not among his desires)