I know your picture isn't to scale, but make sure you have a big enough return area in your sump so you don't have to top off evap every day. Also, having an "over" baffle before the return area will mean that the water falls into the return area - increasing the probability of having microbubbles.
I Mag12 should give you plenty of flow - make sure the pipe from the refugium to the main tank is oversized so it can handle the flow.
Looks good.
-Mike