(1) Donbas - though Russia was not initially attempting to annex this area. The negotiations scrapped by the West would have left these regions as something like special administrative regions under Ukraine, akin to what Russia had already been trying to relatively peacefully achieve for a decade with the Minsk accords.
(2) Coal + industrialization + peasants seeking a better life.
(3) Actually quite a lot happened, but I assume you're referencing the fact that a small number of Russian forces were deployed to Crimea. A practical issue when territory "peacefully" changes hands is deterring the former "owners" from simply coming in and trying to kill everybody to immediately reclaim it. The important issue is whether those forces drove coercion or otherwise manipulated the outcome of the referendum in a way outside the will of the people. This is what the West tried to prove, but they instead ended up proving the exact opposite! Incidentally, a comparable referendum held in Donbas was likely outside the will of the people, and consequently - Russia did not recognize it.
#1 is not accurate. Here [1] is a visual map of the last census showing the percent in each region where Russian is the native language, which is a reasonable proxy for Russian ethnicity. This [2] shows Ukrainian ethnicity by region. That census is also from 2001. It's unclear what happened in the 13 years to 2014, though after 2014 it's safe to say it became majority ethnic Russian due to the constant conflict going on. That area in the East/Northeast is Donbas of course.
Crimea is far easier on #2. Crimea has never been majority (or plurality) Ukrainian. Prior to the Russians it was Tatars, but they were exiled after WW2 by Stalin for collaboration with the Nazis. The reason Crimea ended up under Ukrainian control is because in 1954 Khrushchev 'gifted' it to Ukraine to celebrate the 300th anniversary of the Pereiaslav Agreement. That agreement is when the Cossacks that lived in 'the ukraine' (Ukraine translates to something like at the borderlands/frontier) signed a treaty swearing allegiance to Russia. At the time of the gift it was mostly just a token gesture, because Ukraine was just another normal part of the USSR and so basically nothing changed.
(2) Coal + industrialization + peasants seeking a better life.
(3) Actually quite a lot happened, but I assume you're referencing the fact that a small number of Russian forces were deployed to Crimea. A practical issue when territory "peacefully" changes hands is deterring the former "owners" from simply coming in and trying to kill everybody to immediately reclaim it. The important issue is whether those forces drove coercion or otherwise manipulated the outcome of the referendum in a way outside the will of the people. This is what the West tried to prove, but they instead ended up proving the exact opposite! Incidentally, a comparable referendum held in Donbas was likely outside the will of the people, and consequently - Russia did not recognize it.