Thats a very good way to do it!!! Good design, seems like you have done some research..a gravity system is reported to be one of the best designs.
The only comments on your design are that you may want the refuge to return close to the pump, so the skimmer isnt sucking up the pods...Some are going to die going through the return pump, but not enough to worry about. Where you have the "Y" in your picture, I would add a ball valve so you can regulate the flow to the refuge and set it where you want it. Also don't forget lighting needs to, make sure you have room, etc when designing the heights etc..
You also have the choice, as some here do, of T'ing off the return line to supply the refuge..both work well, and if you search you will see many opinions!!
Your design is sound and proven by many on here, enjoy it and have fun!!
Bill
One other consideration with drilling the refuge return, you may want two holes, one higher than the other to give you a safety zone if the first backs up with caulerpa or whatever..that way hopefully you will catch it before it floods onto your floor!!! Redundancy helps in this hobby!!!