The thing about such a strange environment is that we have no way of knowing how cultures would react to the constantly shifting climates and temperatures in the closer-to-pole areas, because there is nothing in the human experience (on this planet, at least) that can equate to it, that I know of.
My suggestion for these regions is that they are little-explored wilderness areas; perhaps they are claimed as frontiers by the nearest nations but which are pretty much uncontrolled, like much of the USA was during the Colonial period. I would also suggest some kind of mysterious non-human race, suggested at in myths and conjecture, but not really exhibited. Perhaps they have separate forms for both periods of climate or something like that. That also opens plot hooks for the players after the Panama incident- they can go into the North or South and encounter these strange beings, waiting for the Hellwinter or whatnot.
Next on the agenda-
I think that this is an awesome idea, and I would love to be part of the campaign.
I fear to say that I'm not a great fan of the modern names that parents bestow on their kids (Colby, Taylor, Kaira, Jayden). Sorry.
As for place-names-
The Strip (proper term would probably be "narrow", not "thin") could be something to do with the middle- Midland, Middlan, Mydaer, simply Mid, Middoth, et cetera, or you could come up with something totally new. You could name the city a variation of Panama- Paenam, Paanaama, P'anma, Pamam, Punomo, or, as before, something totally new.
The key here, I think, is not to have what I call "Fantasy Hodgepodge Syndrome". In FHS, everything is everywhere. A city named Ffaearean is right next to a city called Szoth'ox or something. A region with a certain language will not have such disparate names, unless they are holdovers from immigrants or something. If you name "Panama" P'anma, could names for the Strip might be I'mid'om, or Mid'dimo, or something like that. Do you get what I'm saying?
Well, that's all I got for now. Looks to me like you have things well in hand.