I understand the armor cap is 567. I just want to confirm that if I achieved the cap by using fortify smithing potions/clothing, perks thats increased my armor rating by x% would be useless.

How would it be useless?.. Lol, just go up to the cap ^^

AFAIK you get no additional protection from damage by improving your armor past the point where the armor cap is reached. Whether you used potions and/or enchanted apparel to get it there is irrelevant. Using them just to get it higher than it already is, once cap has been reached, would be pointless. However getting it up to the cap (or beyond) by any means possible is not.

I've never used the loop through 5 characters. But I think I'm going to use fur this time around until I get dragonscale.. And fur just doesn't cut it on master. I'm using it with a sword and board character.

You don't need to abuse the loop to reach the cap.
If you don't care about matching armor perks, hitting the cap let's you mix and match your gear, wear hoods, etc. Or just pretend their is no cap. Reaching it is not a goal, passing it is not futility. Just play and have fun.