Nah, it's not dangerous for Russia at all. Hitler's concentration camps provided a lot of political fodder for other countries to initiate war with Nazi Germany. If Russia doesn't make that mistake, keeps their conquests slow and reasonably managed (i.e. one front), it would not be too difficult for all of the "West", in particular Russian-dependent Western Europe, to overlook their advances into former Soviet territory.
The U.S. is never going to move, as it would lose all of its Asian interests (Japan, South Korea, Taiwan, etc.) if it commits to fighting against Russia. U.S. moving against Russia is going to spell MAD, maybe not nuclear MAD, but MAD nonetheless, and there isn't enough political capital in the U.S. to want to risk that.
Western Europe is by and large going to do nothing, since they're heavily dependent on Russian natural gas (by Russian design). They've pretty much alienated everyone else who can provide them with natural resources, except maybe Turkey. And it would be a long, protracted war, as history has told us time and again, which they aren't going to initiate if they don't feel sufficiently threatened, and which won't happen if Russia only moves against countries in the former U.S.S.R. Hell, some people in the U.S. probably couldn't tell you the difference between Russia and U.S.S.R.
Nobody's successfully taken over Russia except for the Mongolians. The Chinese/North Koreans will not move against Russia without significant concessions, at which time they will take over the rest of East and Southeast Asia first before aiming their guns towards Russia if at all, since Russia is more of an ally to them than any "Western" country. In fact, I'd say that if Russia does move against Western Europe, and the U.S. is dragged into a long and protracted European front, that it will be more likely Russia+China+North Korea vs the West rather than Russia vs. the West+Asia.
Putin knows this, and that's why he's able to move against Ukraine now and other parts of Eastern Europe later. There's almost 0 chance of war, and if there is, it will be Russia vs. Ukraine, and no one else. Maybe when it was still the U.S.S.R. 30 years earlier, there was enough political capital to commit to a war with the Soviets, but the West is war-weary and the "Western" populace in particular is disinterested in fighting someone else's war at this point.
If things go this route, I suspect it'll be Estonia, and Latvia since there's a sizeable Russian population there. I'm pretty sure it'll be Lithuania, and Belarus after that, to make Kaliningrad contiguous with the rest of Russia. Or, we could be hopeful that Putin will stop with Crimea. I wouldn't count on it though.