Looks like a good start. As for the water barrels, now that you have the filling mechanism, why not buy just 2 barrels, not water barrel setups. Then move one of those existing barrels to the back yard. Place one of the new barrels in front and connect those 2 front yard barrels together. Repeat out back. That should allow you to fill up both barrels out front and once both are filled, it will cut off and send it down the down spout.
Hope that makes sense.