Thank you to everyone for all the well wishes and supportive comments. They're very much appreciated.
We didn't end up taking Hobkin to Athens. Our vet got him stabilized in an oxygen box with periodic Albuterol treatments and gave him a Lasix injection to decrease the fluid in his lungs, but Hobkin refused to eat anything at the vet’s all day. However, when I got there, I managed to coax him to eat a decent-sized (and messy) meal from my hands; the trade-off between overnight veterinary care versus him stressing out and not eating with strangers wasn’t a good one. So he’s at home now in a makeshift oxygen tent. fosteronfilm and I are watching him in shifts tonight. If Hobkin gets worse, we’ll be rushing him to the emergency vet/critical care clinic which has been alerted to expect us. First thing tomorrow, we’re taking him back to our vet's for another Lasix injection and another day of observation in the oxygen box.
I’m cautiously optimistic, but it’s still definitely touch and go. And it's going to be a long night.