They’d have really big eyes. Depending on the wavelength they can see, they might be nearly all eye.
If they were able to see a significant chunk of it at good acuity they’d have to be so big I doubt they could survive in a gravity well thanks to the square cube law of surface area. Be more like living space stations. If they were distributed organisms like a mycelium or Aspen colony, maybe they could survive actually visiting Earth, but they’d be really big. Processing that much data over large areas would mean they are very sophisticated thinkers but with a very high latency so slow.
One fun implication of these building sized to tens of kilometer sized eyes is that am sources would look like a one color light source getting brighter and darker while an fm source would slightly shift colors. Going to earth would be like going clubbing with strobes and disco lights thrown everywhere.
You’ve described the reasons why aliens that see in the radio spectrum would never evolve in the first place. Aliens from a particularly cool star might have their vision attuned to infrared, but no place that’s warm enough to have liquid water would be cold enough to make radio waves more useful than infrared.
Yeah and even functional infrared eyes need to be at least twice the size of ours if not over ten times for more far thermal ranges. Anime eyes. The classic 20/20 D&D infravision would require eyes the size of basketballs, lol. Dark elves would put the innsmouth look to shame.
Larger than they would be for visible light, yes, but not necessarily larger than human eyes. Birds, for instance, can have amazing vision with much smaller eyes.