Regeneration (episode)

I really like ENT regeneration, and think it's one of the best star trek episodes. However, one thing that doesn't make sense is the borg can survive and function effectively in the cold temperatures of space (-270.45°C), and yet they got frozen in the ice and snow of the arctic (-40°C). Why couldn't they survive in the arctic, if they could survive in space? Do you think that makes any sense, and why?

If federation scientists documented the borg on earth, and the borg were on the enterprise nx-01 and captain archer filed a report about them, then why didn't the enterprise d's crew know about them in q who? Shouldn't their advanced scans and computer databases have identified them as a species that was previously encountered by earth, even if the crew didn't recognize them?

If the borg could heal damage with nanoprobes and the shared power of the collective (VOY unity), and even revive corpses that have been dead for a while (VOY mortal coil), then why did the borg drones apparently die after being shot with bullets on the holodeck in first contact, and being shot with phasers throughout star trek (before their shields adapted), since they should just be able to repair damage like that?