the model doesn't matter IK is just a way to solve animation along a joint chain. you wouldn't really use it for arms in a walk, rather just for limbs or whatever that are planted to things, like the feet as he's walking. arms that are swinging about should be keyed in FK as that will make it easier for you to have them…
get rid of IK on the arms don't lift the feet that much, don't keep them flat when they're in the air check your curves at the end, like jordan.kocon said, it's not looping when that's done, you've not only improved it by a ton, but you'll be at a place where we could start talking about more stylistic/artistic choices…