.
You have 64 square feet so you need (64 sq ft X 50 W/sq ft) = 3020 watts for a stationary light, for best flowering.
If you use a light mover you can cut that in half.
.
A 400 watt light leaves a light foot print of 36" x 30"; a 600 watt light leaves a light foot print of 4' x 3'.
For that room I would go 2 x 600 watt on light movers going over cages of 8' x 3' area; 2' running down the centre of the room for working space.
If you don' put up reflection in the middle of the room then have the movers run on opposite rotations so there is light at both end of the room at all times. Not very important but it will help.
.