Looks better (and safer) with handrails. I'm not sure what those "little houses" are exactly, if they should have like a doorway ? Probably. Also it seems that they added cranes for the 3 or 4 stages versions, those are not present on the awesome UR-500 pic @MaxBuzz found. I have no idea what are their purpose, given that the rocket, fairing and payload are already in place on the train, there is no thing like on-pad assembly. Maybe they wanted to be able to remove the fairing and switch the payload if needed ? Maybe they are used to lift some equipment and tools used by the technicians (I'm not sure there are elevators, so it would make sense...), to reconfigure stairs and walkways if required...
Well the long grey structures are actually bunkers, they seem to be made of concrete and designed to endure a bombing run or a very misbehaving rocket. The UR500 was supposed to be the mother of all ICBMs so having big storage bunkers near the pads make sense.
By "houses" I meant the metal "boxes" you have on each side atop the mobile tower, not any ground structure, those are rather well documented in the ILS manual.
Back on the tower, working on the "false ring" (or ring 6 1/2, a bit like train stations in Harry Potter ), looks like some scaffolding between rings numbered 7 and 6, also continuing the staircases and handrails :