You can use check valves, but I would caution you for relying on them in a salt water aquarium. Over time, little tube worms and other creatures will line the walls of your plumbing. These prevent the check valve from sealing properly. I haven't used them in years.
One thing you will want to do is simulate a power outage. Turn your pump off and see what happens to make sure your siphon break works and that the sump has enough volume to contain the extra water that will flow into it. Better to do this when you are present than learn the hard way after you wake up to a flood!
I would also put a float switch on the pump that shuts it off in the event the sump runs dry or near dry. Some of the modern pumps have this feature built in but your Mag pump does not.
Dave