You need to figure out your return plumbing length. Add 1' for every 90 degree turn and 1/2' for every 45 degree turn to get your total length. Take that number and go to Sicce's website. When you find the SDC WiFi product line, there should be a chart with the various pumps and flow rates @100%. Find your pump and where the height intersects. That's your revised flow @100%.
You typically want at least 3-5x the flow of your total system volume, so if you calculate those numbers and compare to the chart you should be able to approximate a rough starting percentage, ie: 40%. You can always have more than 5x flow - so some of this will be trial and error (particularly once you add corals).
I run my SDC 9.0 @45% on my 200-gallon system, which works out somewhere between 3-3.5x my total system volume. I also have oolite, so any faster and sand starts getting blown around the bottom.