The thunder hammer wielder and his base look great! As for his left hand, frost claws will get in the way when he wields the hammer. Best give him a shield; or a pistol with a chain linking its butt to the Space Wolf's shoulder (see lanyards used with real world pistols for reference), so he can lay down suppressive fire as he charges forth to bring the enemy within reach of his hammer, the lanyard preventing him from losing the pistol when he releases it so he can wield the hammer with both hands.
I do have some wrist mounted weapons from the Blood Angels Sanuinary Guard kit and also the Grey Knights that might fit in well - will give them a try.