Still, IKC, that combined potential was basically the entire lightside...and it was pretty much said trying to actually fight the force storm would be useless...they pretty much shielded Sidious from the Dark Side, causing him to lose control of it. As a dark sider, Kun would be incapable of using the light in such a way unless he had a last minute epiphany
Depends. If Kun has a way of countering the blast (I wouldn't put it behind him, we do know the Ancient Sith had a form of the technique, so there should have been a way to counter it in one shape or form. Whether he knows that technique, and can use it against Palpatine on a larger scale, is up for debate).
I say Luke goes down hard and fast, and Palpatine's force storm, and whether is can be blocked, however, is up in the air.