The inner side of the radiator would be metallized, an anti black body. Together with a bit of vacuum it would thermally be quite far from the PV&GPU. Thermal insulation is easy in space.

You still can't get more surface area than a sphere without crumpling things up. And given the thermal insulation, you can only lose heat via radiation. Radiating heat from a crumpled boundary means radiating it towards another part of the boundary. If there's an "inner side", then it's a sphere (or some other convex shape, all of which have at most the surface area of a sphere).

I don't think you'd want any vacuum at all between the radiator and the heat sources! Thermal insulation is the problem, not the solution. You want the radiator as thermally close to the heat sources as possible, probably via some highly heat conductive metal.

Though the optimal approach might be to ditch the vacuum and use a more terrestrial configuration with circulating air or water or mercury to conduct the heat away. Space is a horrible place to do this in all ways except for... well, space. You do have plenty of room up there. (Well, and power. Lots of solar energy to play with. Which in turn causes its own problems with heat and radiation.)

With a heatpump the PV and GPU would have the evaporators, the radiator would have the condenser. You do this for two reasons, so you can run the radiator hotter (4th power and all) and because the refrigerant is a good heat spreader (better than pure liquid cooling).

With a heatpump, you don't want a thermal bypass, hence the isolation.

Space is not a great place to get rid of heat, but if you need lots of surface area any way for PV that almost solves itself.