All your concerns are good ones, if these are going to be reef tanks.
If you plan to raise fish in these tanks, then there are no snails and no concerns. Plumb your return through a central manifold, have a pressure relief valve T'd off the return before the manifold, going back to the sump. Remember, for a fish only tank or tanks, flow is less of a concern than for coral containing tanks. You don't need the monster pumps, hundreds of gallons per hour, etc.that you may need for a reef tank. From the manifold, plumb the return to each tank, including a ball or gate valve. Have the overflow pipes be bigger than the return size, and you are good to go.