-- Does Russia have any moral high ground in this? Nope. Look up, eg: Holodomor. People will say, "But, that was the Soviet Union!" Whether or not anyone wants to believe it, the Soviet Union was far more synonymous with Russia than sophisticated people want to admit. (Former President Charles DeGaulle of France made no bones about it, and referred to the Soviet Union as "Russia" 'til the day he died in 1970.) There are reasons for which the cities of the "Republics" of the Soviet Union were aggressively Russified during the period of the Soviet Union's existence.
-- Russia still needs to disavow the Soviet Union and its depredations in as emphatic a way as the Western World has anathematized Nazi Germany. Russia, and the Western World need to reject what we understand as Leftist Socialism with the same vehemence and revulsion as we condemn Naziism (which is qualitatively no different from Leftist Socialism anyway).
-- Does Ukraine deserve to be independent? As a result of the Holodomor, yes. Absolutely. Because of the Holodomor, Russia has lost all moral authority for at least six generations. Long enough for people to stop being bitter about the treatment of their ancestors in history.
-- Does Putin reasonably have anything to worry about from Ukraine as it pertains to security or anything else? Nope.
-- Does Putin reasonably have any worries about anything coming from his West either to threaten Russia or him? Nope. Does Putin know this? Of course he does.
-- Can Putin use Russia's history as an excuse to pretend that he is a Great Russian nationalist with genuine concerns about aggression coming from the West? Sorry, he cannot – not legitimately, anyway. Will he? Of course he will.
-- Does Putin reasonably have anything to worry about internally, coming from say, supporters who might believe Putin to be beholden to them? Yes, absolutely.
-- Could this Ukrainian adventurism be a way to nullify those internal pressures for a while? Absolutely.
-- How about from the East? Are there potential problems emanating from Russia's East? Yep. China has been engaging in expansionist behaviors for years now in the South China Sea, as well as politically in Africa. Look for China to do the same politically in the Central Asian Republics.
-- Could this Ukrainian adventure be a feint to the West to throw off the genuine menace from the East? Absolutely. And, let’s face it, this idea has featured in the discussions of Russian higher-ups.
-- Can the West reasonably expect to prevent Russia from essentially re-absorbing Ukraine into Moscow's orbit? Nope. I'm very sorry to report that.
-- Is the incursion into Ukraine vital to Russian interests for anything? Nope. Not a blessed thing. Vital, no. Beneficial? Sure.
-- Pursuant to that, what benefit(s) will the re-absorption of Ukraine into Moscow's orbit provide to Russia? Well: Ukraine's fertile soil could feed the world something like ten times over. (Note: Watch out, oil-rich Central Asian Republics! Hence, China's interest in that region. as well as in Africa and Southeast Asia. Russia has loads of natural resources and doesn’t need the Central Asian Republics, but they’d love to be able to restrict China’s access to them.)
I know a whole lot about more recent Russian history and culture, a lot about less recent Russian history and culture, and some about even the less recent. And I wouldn't feel confident in telling anyone precisely how to respond to the Russian incursion into Ukraine.