1. A so-called "Puppet Government" never works, unless Russia is willing to station troops in Ukraine for the long term to keep the puppet in place. If Russia can't even buy enough PGM for her own aero-space force to use lavishly (as witnessed in this war), what do you think an occupation force would cost? It will be a true "人民战争的汪洋大海".
2. As long as the West is NOT directly involved, there will be NO meaningful ceasefire for Russia and Ukraine. Because the West will simply keep up the sanctions. Even if the Ukrainian government of Zelensky relents and agrees to capitulate to Russia, the West could still treat his government as either illegitimate or "held hostage". The sanctions will extend to Ukraine, exasperate the economy, create more social instabilities which will only take a toll on Russia.
3. Putin's plan was flexible enough to begin with, they tried for a quick win, ONLY with the assumption of a low level of will to resist from both the military and the civilians in Ukraine. If that turned out to be not true, then a quick win would have been impossible even if Russian forces are much larger and much more capable and advanced. Because this war is not just a pure tactical war, it is also a political war. (Technically, all war are political). The US's wars in the Middle East only seem more "successful" and "mighty", because the countries she fought had enough internal problems and a lack of modern unified national identity. (In other words, Middle Eastern countries that the US fought in the last 20 years weren't technically "Nation States" (民族国家) , by strict Western Sociological Standards).
4. Even if Putin was able to "shock and awe" Ukraine in a successful "blitzkrieg" (whatever you meant by that), there WILL be subsequent problems with policing and occupying the defeated Ukraine. Because you can't defeat and conquer the collective identity of the Ukrainian people, nor is Putin planning on doing so, nor does Putin know how to do so.
In conclusion, realistically speaking, Putin's only meaningful goal, is to destroy Ukraine's defense/heavy high-tech industries, destroy the fighting capabilities of the current ultra-nationalist (extreme right) fighting forces of Ukraine, AND help set up as many REAL (well organized and with a integral population base) separatists subregions (aka. "people's republics") in Ukraine.
Other than these three goals., everything else is NOT realistic.