One return would be my preference but you can do two if you want. Again, your shorting for an overall turnover of 3 to 5 times your system per hour. Whether that happens with 1 or 2 pumps is up to you. When looking at pumps, check the pump curve graphs/charts to see how many gph pump will do at a given height. Guessing the top of your tank is about 4 feet so you'll want something that pumps +\- 600 gph at 4 feet.
Not sure that split drain to the refugium is going to work. You should T off your return pipe to bring water to the fuge section. Both drains would then go to the skimmer section. Keep any turns and Ts in mind when figuring out your return pumps output as they add to head loss. Use valves in the return line to help dial in the flow as needed.