I would try to buy a complete kit from someone if you are unsure or ask the manufactuer of the fan.
They may ask a few questions because fan type and airflow are gonna make a difference here.
Such as do you have ac, air to air or water to air intercooler, internal or external oil cooler.
One that comes on and then ramps up or 2 fans on a staged relay system are typical setups.Just switching it on and off may not provide the best efficiency and cooling characteristics.
But if you just switch it on and off I would try to keep the engine as close to normal operating temp as possible for daily driving.
If you are racing maybe go with the cooler setting.