Caribou, think big deer. They are not nearly has hardy as an elk.

Bullet wise I would probably stick to one of the hard cast bullets as that is my personal preference. My 480 seems to really love the Beartooth 420 LFNGC bullet over 19.5gr of H110. That load is way more than what is required to kill a caribou but shoots most accurately out of my SRH. If you happen into a pissed off brownie, that load will pull double duty as a good SD load.

The 480, like a 44M out of a revolver is really a 120yard gun at best. Beyond 120 there is still more than enough energy but the bullet is really dropping fast.
That being said, I would pick a tube type red dot over a traditional scope. Either an UltraDot 30 or a MatchDot (although I don't think the MatchDot will fit between the Ruger rings).
With a dot sight I am more than accurate enough at 100 yards to be lethal, no magnification needed.