Not just Slavic. The entirety of ex-USSR (a good half of which wasn't Slavic), plus countries in Eastern Europe such as Romania.

Sure, but two things. No one is contesting their Central Asia client states that's in their pocket --we're not trying to expand NATO there... and two they have a special affinity to Slavic peoples due to culture. (they treat them like an "ex-" with a certain amount of jealousy.

Central Asia, no (although China is actively making inroads there).

But there's still Armenia, Azerbaijan, and Georgia to consider. These aren't Slavic, but they are of interest to both NATO and Russia. Well, Armenia is pretty firmly aligned with Russia for historical reasons and some semblance of security against Azerbaijan and Turkey. But the other two are already Western-oriented, and Georgia has applied for NATO membership in the past.

As far as Slavic affinity, it's a bit more complicated. For example, Bulgarians are Slavic, and Eastern Orthodox even, but being on the wrong side of WW1 and then WW2 vis a vis Russia/USSR overrides that. OTOH with Ukrainians, many Russians outright deny that they even are a separate nation or ethnicity, and claim that it's just a sub-branch of Russians who speak a dialect of Russian. From that perspective, occupying Ukraine is described as "re-unifying" Russia.

(Source: am Russian)

I wouldn't make it about ethnicity. Making it about former Soviet republics and members of the Warsaw pact is the problem, from Russia's point of view. A problem that, in hindsight maybe, is so obvious and so guaranteed to come (Russia complained about NATOs eastern expansion for decades) that it seems surprising that NATO doesn't seem to have an answer. Hell, when Russia annexed the Krim and tried to annex parts of Georgia one would think NATO would have gotten a clear wake up call.

Well, the problem is even worse in EU.

Germany makes deals with Russia to get their gas (NS1 and NS2) and only recently they declined NS2.

Basically we (EU) are giving Russia money to create army, instead of ditching their gas, oil etc. and buying one from Scandinavia and US (now when Russian gas prices are higher than the ones form the mentioned countries). And destroying NS1 and 2.