newbie piping questions - what size return - what size overflow?

[golf nut]

Until we know exactly what size holes are drilled already it is difficult to determine what is the most effective way to continue, if indeed they are 2" then a Herbie will be fine, it isn't possible to have the secondary drain of 1 1/2 flood with the pump size you are considering I doubt any saltwater pump with a 3/4 outlet could get a 1 1/2 drain to kick into siphon mode..

Having the sump returns at the other end is perfect and should still leave you a little window for the refugium, just make sure the refugium drain is large enough to handle all the flow from the return pump should something happen to the sump returns.

ps the sump returns should have elbows on them to move the surface water down the length of the tank, as long as they are just below the surface siphon breaks are not required..