So, I really, really like 1 and 2 the radial symmetry makes great sense for a space station, the style in which it expands feels very organic, but I don't feel as though 3 captures the scaling up that 1-2 did. Three has as much more mass as 2 added to 2, but not the complexity of mass?
And four, on those same lines, seems even less of an expansion of the base from 3-4 than 3 was from 2. So, why does it feel like upgrading your core gets you diminishing returns?
I'd go so far as to suggest swapping the central cylinder for the bigger, rounder cylinder at some point, and possibly stacking another ring segment. Another thing you can do is extend the conning tower from the top, like many bases do as mooring-points. Later, a base can grow towers around it, like the kusari bases often have.
You can keep it a narrow rod, and keep adding height and slowly thickening it, or you can go for big spokes and rings, but I'd really suggest maintaining a general sense of radial symmetry.
Of course, if we go to a 1-10 core size system, then 3 and 4 being less huge improvements is likely fine. Scaling always feels different on different scales.
