A sparge arm is a folly. If you want to fly sparge, I'd recommend using a manifold for your return.
So just swap out my kewler screen for a copper or PVC manifold set-up and go slow, huh?
The general consensus is to have a half inch of water on top of the grain bed, staying consistent with the amount and speed of run-off. You don't need any special whirligigs or manifolds for this.
I usually drain nearly all the mash first, then fairly slowly fill up the tun with water until I have some hot water across the surface of the grain bed and then start a very slow run-off. While doing this I don't disturb the grain bed by stirring, but I have found that cutting the grain bed with a long knife or spatula not quite all the way down to the false bottom (thanks, Gordon) keeps the water from making channels in the mash.