1) Why is Russia Doing this?
The Russian invasion of Ukraine has very little to do with Ukraine's ties to NATO (it wasn't allowed in despite years of trying) nor due to Western "provocation" (well refuted here), rather as Putin himself has said numerous times, a desire to recreate the Soviet Union, this time as a Russian nationalist project as opposed to an atheistic, ideologically communist one. To that end, Putin is playing up his role as a savior of all Slavs both in and around the region.
To understand why Russia wants to restore Soviet era borders please watch this excellent video on this topic:
As the video clearly states, Ukraine (along with Moldova and Belarus) becomes part of a security zone for Russian central plains (where 80% of Russians actually live). Carpathian mountains, Crimea and Kalingrad are choke points.