I think the one thing you got wrong is that the invasion of Crimea was a response to economic troubles, not the cause of it.

Russia spent ten years doing what the IMF said, which was essentially implementing Reaganomics. That could not work for the same reasons as it didn't work in the Western world, long term. But short term, after Putin took power, it started generating results. Privatization led to industrial resurgence and a generally favorable climate for fossil fuels pumped money into the economy.

After ten years, it was becoming painfully obvious that Russia was rich, but Russians started to be poor. So Putin started blaming NATO, the EU, and the West in general for hardship, like all fascists do when they are running out of excuses.

Invading Crimea was a way to give Russians a reason to suffer through the economic pain. Just like in current America, the economic pain could not be fixed, because the oligarchs were sucking up all the money. It may be a little more complicated than that, as the Crimea invasion was also a crime of opportunity, after Ukraine had shaken off a Russian puppet government.