Hiyas,
I just thought that I would chime in here and give a few of my own thoughts
You should NEVER restrict the discharge on a centrifugal process pump with a valve at the pump,
NEVER. When the discharge is restricted near the pump, the pump immediately begins to operate off of the best efficiency point (BEP). This creates a radial force on the impeller and attempts to bend the shaft. This is just the laws of physics and it cannot be avoided. Any pump running against a discharge valve that is throttled back will have a decreased life expectancy, however long or short.
Instead, you should probably run a discharge bypass in the event that your pump is making too much flow. Install a T fitting on the discharge line as it makes its way up towards the display. You want the T to be just past the top of the sump. Install a valve just past the T fitting so you can decrease the flow to the display as needed. Run a line off of the T fitting back to the top of the sump. This will allow you to control the flow that goes to the display and let the pump operate at or near its BEP as well. You can also divert all of the flow back to the sump when you need to perform maintenance or have any other tasks that require a calm tank.
How much flow you need really depends on what you would like to keep! Good luck!