Interesting question, they are sparse but I don't have a definitive answer but I'll chuck in a few random thoughts anyway.
If we're looking at some of the Forward Operating Bases (and I do know Engels isn't) with aircraft just rotating through you'd probably not expect much in the way of major buildings....
As for the main bases such as Engels - I do remember the likes of Upper Heyford, Alconbury etc, were massive in comparison even with neighbouring UK RAF bases... so I do wonder if a better analogue in terms of airfield and domestic area size might be one of the old RAF V- Force bases such as Waddington or Scampton, both adjacent to Lincoln (UK 😉).
Even those RAF airfields had attached communities that resulted a sizeable domestic area with married quarters (MQs) etc , so I'm left wondering if in the Russian's simply don't do accompanied postings and everybody is rammed into a few barrack blocks or OTOH everybody is accommodated off base and so there isn't a formal recognisable domestic site, easily identifiable from the air...
As for maintenance facilities on the airfield itself...Again don't really know... I do know engineers can do a fair bit of basic routine maintenance out on the ramp - happens a lot in the civil world, but you'd sure as heck need shelter in a Russian winter...but what happens if you need deeper maintenance? Civilian world at your main base and at the RAF stations mentioned upthread have at least a handful of hangars but as you say there appear to be zero similar on many most of the Russian fields. Do they simply either fly aircraft off to perhaps to a main maintenance base somewhere for routine deep maintenance...failing that?
I have had just one thinks bubble BTW -> big span hangar roofs, Russian construction and Russian winter snow.... are they a winning combination???).
So in summary...don't have a definite answer....I'll have a dig round..