It's not even funny to talk about NATO build-up. You'll understand it when russian soldier breaks into your house or his rocket blows up your house so you don't "humiliate russian speaking people".
Re Syria: NATO was bombing in Syria for years and it didn't have (and still doesn't have) any legitimacy to do so - neither by the UN nor by the syrian government. Russia was invited to help by the elected government officials and this has the legitimacy to be there.
2. Constitution of Ukraine states that only citizens of whole country and not only locals can decide such questions, _ANY_ local referendum regarding sovereignty is illegal.
It is how russian troops work and it is not legal anyhow.
Re Syria: it might sound good but when we track who russians are bombing we might notice that it is just helping Asad to save his power by killing all people who want freedom even civil ones. In the end russia is supporting isis by supporting Asad.