Would these boots be suitable for all day mountain hiking? Supportive? Blisters? Do your feet get cold near the rubber?

I would only use these on a very gentle hike. I find the soles don't grip very well on slippery surfaces and, unless you're wearing very thick socks, the fit of the boot is a bit roomy in the toe and ankle area for serious hiking.

You could hike in these, but they are not technical boots (i.e., they are not mountaineering boots) and should be confined to winter walking and light hiking. I have gone winter backpacking in a North Face equivalent boot and it was fine--but the terrain was not steep. I can't speak to how supportive they are. Footbed support is easily achievable by replacing the footbed with a high-quality aftermarket insole like Superfeet or Sole. (You actually bake Sole footbeds in your oven so that you can mold them to your feet; Superfeet mold themselves to your foot over a few days without baking them. Both are excellent.) Blisters shouldn't be an issue if your boots are properly sized to your foot and you are wearing the appropriate sock/sock layering system. I would be very surprised if Sorel didn't account for rubber's ability to transfer cold and therefore ensured it wouldn't be an issue. Hope this helps.