what size to make intake for air cooled lights??

i have a 12inch vortex fan cooling 4 1000watt 8inch aircooled lights. what size should i make the intake 6/8/12inch? im cutting the hole in the floor should i make the hole 6inch and reducers to a 12inch to the fan, reduce the 12inch from the fan to a 8inch go threw all lights then back to 6inch for outake, i heard reducing the diameter of hole speeds air flow is this true?

Reducing the diameter after the fan will increase the air pressure/air velocity, but you're gonna want to keep the intake side the same diameter as the fan. Making it smaller will only decrease the amount of air available to the fan, as atmospheric pressure is the only thing feeding it.