Pump/Powerhead?

Look for a pump with approximately 900gph output at 5 foot head pressure (the height which the pump is pushing against). This is the amount of space you will have between the bottom of your sump (where the pump will be) and the top of the 90 gallon display.

While you should not really restrict flow very much on a return pump, people do it often because it is somewhat difficult to find one for your exact situation. most people find what's closest to the size they want, then dial it down with a ball valve until the water flow is low enough that the overflow drain stops gurgling (taking in too much air). One way to overcome this issue would be buying a variable speed return pump. You can set it to the amount of flow you want using the dial on the front of the pump and it will work accordingly. Tuze makes their own version of this and it can be found here.

However I would not suggest a check valve at all just because they are so prone to failure. Allow enough room in your sump for some back-flow from the display without the sump overflowing. I would estimate this to be about 5-8 gallons depending upon how low you have your return output beneath the water line (in display tank). If your return is drilled this will be easy. Just use lock-line and aim the nozzles toward the surface of the water for agitation and very little water will be able to drain when the pump is turned off.