Also a general tip on overflows.. it might seem like you want a large diameter one to prevent clogging (snails, algae) and to handle flow, but actually a thinner one creates a faster flow that can carry air bubbles down and out the drain instead of staying at the top of the overflow, ready to break your siphon and overflow your tank. So TWO smaller ones might be good, so you have backup.
Set up a float switch to shut off your return pump if necessary.
When I started in the hobby with a nano reef, I flooded my apartment about 5 times.